HOW TO FLASH
well described by the developer himself on the main thread , post #3
down below is the user`s experience as following
_*HOW TO FLASH MONX's ROM (4.4.2) v5.0.3 BASE 681*_
*FROM 4.2.2 BASE 534 for model C6903*
*_Files needed to update to 4.4.2_*
Grab flashtool from here
Grab the root tool VROOT from here
Grab recovery from here
Grab Monx's 681 rom from here
And finally the FTF file from the mega collection here (you can try stripped FTF files but some people have had problems and I have personally tested this method and it's proven to have worked)
The one I used was this one
1. First things first, back up your internal memory.
2. Next if you haven't already install flashtool on your computer.
3. Copy the FTF files into the firmwares folder
4. Power off your phone and run flash tool
5. Connect your phone whilst holding volume down to enter flashmode, flashtool will notify you that you're connected in flashmode.
6. Click the lightening bolt in flashtool then click flashmode, then ok
7. Find the 534 FTF in the list and click flash (this will wipe your internal memory so make sure you did that back up)
8. Once it finishes, detach the cable and power on the device
*Note! at this point your IMEI might be missing, don't worry about that for now just continue*
9. Switch on USB debugging and unknown sources on your device
10. Run the Vroot tool that you downloaded earlier and root your device, it's all in chinese but it's straight forward enough.
11. Once you're rooted, you'll need to install your recovery so go ahead and run the bat file installer, your device will show a request, just click authorize and reboot when in recovery.
*_If everything has gone well then you'll have a recovery and you'll be rooted._*
12. Now copy the 681 Rom from Monx's thread to your internal memory and reboot to recovery.
13. Perform a full wipe in recovery Data / Dalvic and Cache
14. Install the rom with a full wipe (not 100% needed but I like to be sure) 2nd option in aroma
15. Go back to recovery once it's finished and power off your device then re enter flash mode (hold vol down while reconnecting it to your computer.
16. Re-open flash tool and flash your desired 681 FTF file via flashtool, I went for the global FTF which can be found here although other people have confirmed that others will work.
17. To flash this deselect all wipe options and exclude only TA and system *_IMPORTANT_*
18. Begin flashing the FTF file.
Once that's completed you should be on 4.4.2 and everything should be working as expected.
This is for people who are just looking to start from fresh, if you're already rooted and are already using Monx or a similar rom then you can skip steps 1 - 11.
If you experience any issues after installing the ROM then start from 1.
thank you @dladz