[AC Question]

please help to revert back to official kitkat from lolipop in LGG2

[VidJunky]

I'm sorry that isn't possible unless you root your device. The updates on stock devices are not revertable. If you are interested in rooting the device to achieve the downgrade check out XDA Developers. There they will walk you through step by step instructions for rooting your device and installing custom and stock ROMs.

If you are having issues with the update post what those issues are and perhaps there is a less drastic fix for the issues you are having. I will say this too, in the past, not so much with many of the latest incarnations of Android, factory resets were the norm after major OS updates. We don't see them as much anymore but occasionally something won't take properly or there was an issue during download or installation that caused a bug or two in the update, and factory resetting the device will cure that. The reason this is true is because with the OTA update they have designed the update to remove, change, alter, or otherwise add things to the OS that is running. The reason for this is so that you don't have to do a factory reset, loose all of your data, and have to set the device up again. With the factory reset though you are installing a complete version of the OS in whole, not parts and pieces.

[Rukbat]

I don't know about the G2, but most LGs can be reflashed downward. You just flash a 4.4.4 (or 4.4.2) ROM. As VidJunky said, go to G2 Q&A, Help & Troubleshooting - XDA Forums or the appropriate carrier forum at LG G2 - XDA Forums for help.

(You can't "revert" an update - KitKat isn't in your phone any more, it's been replaced by Lollipop.)

You will lose all your installed apps, data, etc., so back everything up first - see Backing up an Android Device.