If you are still on android 4.0.3 (Ice Cream Sandwich, follow my other guide: ICS GUIDE
ALL in one!
So for rooting Jellybean i haven't found a proper root method yet, so that means we are going to flash a pre-rooted kdz file!
In this case this pre-rooted kdz file also contains unlocked bootloader and CWM so this is much easier.
1. Download kdz updater (attatched below)
2. Be sure to first install msxml.msi or else you will get crash during the update process.
3. Download the all in one kdz file, this contains firware version 20D Baltic with root, unlocked boot and CWM recovery. (comes in all languages)
4. Make a backup of your phone, contacts etc. (optional)
5. Once you downloaded everything, take your phone out of your pocket and turn it off.
6. Hold the "-" volume button and connect your phone with your pc (make sure you have all the drivers installed)
7. Now your phone should be in emergency/download mode
8. Now we are going to install the new firmware, open up KDZ_updater.exe and set the type to: 3GQCT and phone mode to DIAG
select the kdz file you just downloaded (20d+root + cwm.kdz) and click "launch software update".
9. KDZ updater will probably crash, this is normal, that means that it is finished the last code you will see is something like "wparam: 100"
10.If everything went well your phone should reboot and launch in the new firmware. Download "superuser" from Playstore.
When your phone is bricked you can just follow these steps again to unbrick your device.
Installing custom roms
1. Download the custom rom you want and place it on you phone. (Preferred on external SD card)
2. To install custom roms you have to go into CWM (clock work mod). you can enter CWM by going into terminal and type "su" and then "reboot recovery" OR turn your device off, then press volume"-" + home button + power button until it vibrates and shows LG logo then release only power button and keep pressing both of the others for about 8 seconds then release.
3. While you are in CWM you can navigate with the + and - volume buttons and the power button is enter.
4. Before you install any new rom, wipe everything from your phone by going to "mounts and storage menu" --> format /cache, /data and /media, /system, /sdcard, then wipe the dalvik cache under the advanced tab. If you don't do this you can get problems!
So now you can select your customrom.zip and press the power button, your rom will now install. after it is installed you can reboot your phone and if you did everything right your phone should boot into your new rom, the first boot can take a long time sometimes.
Some custom roms for jellybean:
If you want a ICS based rom like cm10 or MIUI you first have to flash v10 baseband attatched below.