KitKat the EASY Way!!!!
Or, go back to 4.2.2
UPDATE: KitKat WITH Root the EASIER way. - Thanks to
AndroidUser00110001
WOW, Things are moving FAST!
UPDATE:
For anyone looking to do this, there is now an easier method to get KitKat on your phone and KEEP Root. See AndroidUser00110001's thread here: http://xdaforums.com/showthread.php?t=2665391
The difference between these methods is that you can use his method just like flashing any other Custom ROM using Custom Recovery like TWRP or CWM. Only difference is that you are flashing the Stock OEM KitKat ROM.
When you use my method here, your phone is WIPED. When you use his method, you would wipe like you normally do when flashing a Custom ROM, but you don't have to wipe the Storage Card space, so your data will remain intact. (Of course, ALWAYS backup before modifying your phone, just in case)
If you are going to return your phone back to warranty, I would suggest my method in this thread as it does a COMPLETE wipe of your device and puts it back to 'Factory'. It removes Root Flags so it does not show having been rooted, and removes ALL data.
If you already have a Custom Recovery on your phone and want KitKat quick and easy, use his method. 
Disclaimer: This is not MY method, but a methods I used. The information and files have been figured out over time by many individuals and it's been combined in this thread.
This thread is to help Noobs AND Veterans to flash their ATT D800 LG G2 to KitKat. This will be very spelled out, and I’ve even included a video, so NO Mistakes. Yes, that means you!
PLEASE refer to the Video Below before asking questions, as too many questions get a little overwhelming.
Warning! Please Read!
This WILL erase everything on your phone and put it back to FACTORY STATE, so be sure you’ve backed up! At the time of this write-up, the KitKat version does NOT allow Root. Root is not available for KitKat, YET. If you want Root, you must flash the 4.2.2 version, root that, and then call or get on Online Support Chat with ATT and ask them to Push the KitKat update to your phone. After the ‘Over The Air’ KitKat update, you will still have Root, but only if you’ve started from a fresh install.
Ok, first thing you need to do is download the version you want. I’ve got KitKat 4.4.2 version D80020c, and I’ve got JellyBean 4.2.2 version D80010o. These are VERY LARGE files, so be patient, although I am able to get as much as 6MB/s download speeds from this server.
Download Installer - KitKat 4.4.2 D80020c - This Flashes Stock KitKat, WITHOUT Root, and WITHOUT Recovery. - At this point, you cannot add either.
Download Installer - JellyBean 4.2.2 D80010o - Install, then
ioRoot23, then OTA Update to KK. With this version, Custom Recovery gives issues. But, if you are going OTA to KitKat with Root, this is quicker.
Download Installer - JellyBean 4.2.2 D80010d - This is for those who want to install Custom Recovery and not update to KK... Remember, you cannot keep Custom Recovery in KK, Not YET.
Now, for the fun stuff (You may want to print this out for reference and check them off as you go)
Step #1: Program Installation:
1. Save the installer to your desktop
2. Run the Installer by double clicking
3. Wait a while for everything to extract (It might look like nothing is happening. This can take a few minutes, be patient, it’s HUGE)
4. (On Win7 or Win8, Accept User Account Control)
5. Accept my License
6. Don't Change Anything and click ‘Install’
7. Wait some more… and more… Large files are extracting…
8. When it pops up, click ‘Next’ to install the LG drivers. Even if you’ve already installed them, install again! This is to verify you’ve got the right ones installed.
9. Click ‘OK’ to finish the Driver install
10. Click ‘Next to install the LG Flash Tool
11. Don't Change Anything and click ‘Install’
12. Uncheck ‘Run LGFlashTool 1.8.1.1023 and click ‘Finish’ (If you forget to uncheck this, just close the program when it opens)
13. Click ‘Next’ to start the LGFlashTool Patch. (This makes it so you don’t need to change the date back on your PC)
14. Click ‘Next’ again
15. Click the bullet to ‘Agree to my License’ and then click ‘Next’
16. Don't Change Anything and click ‘Next’
17. Click ‘Start’
18. Click ‘Next’
19. Click ‘Exit’ to finish Patch Installer
20. Congratulations, Program Installations are all DONE!
Step #2: Place Phone into Download Mode:
1. With phone NOT plugged into a USB Cable, Hold the Power button to turn off phone
2. Plug your USB cable into your computer
3. Hold the Volume UP Button on your Phone
4. While Still Holding the Volume UP button, plug in the USB cable to your Phone
5. Continue to hold the Volume UP button until your phone enters Download Mode
6. If this does not work, pull the USB cable and start from #1 of this section
Step #3: Change Com Port to 41
1. With your phone STILL in Download Mode and STILL Plugged into Computer
2. Go into Device Manager
---a. Press and hold your Windows Key (Between CTRL and ALT)
---b. Tap the ‘Pause/Break’ Key (Usually Top Right of Keyboard, might be different on yours)
---c. Click on ‘Device Manager’
3. In the Device List, scroll down to ‘Ports (COM & LPT) and double click to expand
4. Find the ‘LGE AndroidNet USB Serial Port (COM4)’ (Your COM Port Number might be different, that’s OK)
5. Double click to open the port
6. On the Tabs at the top of that screen, click on ‘Port Settings’
7. Click on ‘Advanced…’
8. Click on the Com Port number to drop down the list
9. Scroll down to ‘COM41’ and select it
10. Click ‘OK’ Button to save that
11. Click ‘OK’ Button to close the Com Port Properties
12. Close the Device Manager
13. Close the System Window
14. Go back to the Desktop
15. That’s it, You’ve Changed the Com Port to 41
Step #4: Run LGFlashTool:
1. Double Click the ‘LGFlashTool’ icon on the Desktop (Win7 or Win8 accept ‘User Account Control’)
2. In the ‘Model Config’ window, check the box ‘Select Manual Mode’
3. Next to the DLL space, click the Three Dots ‘…’
4. Select the DLL file named ‘LGD800_.....v160.dll’
---a. For 4.4.2 KitKat, select ‘LGD800_20130811_LGFLASHv160.dll’
---b. For 4.2.2 JellyBean, select ‘LGD800_20130904_LGFLASHv160.dll’
5. Click the ‘Open’ Button
6. Next to the S/W space, click the ‘Remove ALL’ Button
7. Next to the S/W space, click the ‘Add’ Button
8. Select the tot file for the version you are flashing
---a. For 4.4.2 KitKat, select ‘LGD800AT-01-V20c-310-410-FEB-02-2014+0.tot’
---b. For 4.2.2 JellyBean, select ‘LGD800AT-01-V10o-310-410-OCT-19-2013+0.tot’
9. Click the ‘Open’ Button
10. Click ‘OK’ Button to save choices
11. In the LG FlashTool program, click the ‘Yellow Arrow’ pointing to the Right.
12. Wait for the program to verify your DLL and TOT selections (This takes a while)
13. If successful, you will see ‘READY!!’ on ‘Port 1 (COM41)’
14. If you DON’T see ‘READY!!’, you may need to start over
15. If you see ‘READY!!’ unplug your phone from the USB cable and Plug it right back in. DO NOT PRESS ANY BUTTONS ON YOUR PHONE. It should STILL be in Download Mode.
16. The LG FlashTool progam will now start flashing your phone!!
17. At around 80%, the program will restart your phone.
18. It takes a while for the phone to restart, but it will boot to Android. Wait for the flash program to finish and it will turn your phone back OFF. And give you a ‘SUCCESS”
IF for some reason, the LG FlashTool does not finish 100%, and you get a ‘Fail’, as long as your phone has now rebooted into Android, you don’t need to worry about this. Just close the program, and enjoy your Freshly Restored LG G2!
For anyone having issue with the device check not passing due to mismatched device (caused by flashing wrong device model to your D800), try using the attached dll file instead of the device specific one. It has been reported to work for many... You will need to extract the zip file to get the dll.
