How to pimp your LG G2 with the all-new flat Optimus interface from the G3
1. Root your LG G2, if you haven't done this already. Be forewarned that rooting may void your warranty, prevent you from installing OTA updates, make you bold, and other assorted problems, at least until you roll it back. Check out a brief video tutorial on rooting the G2 if you encounter problems.
2. Flash TWRP, Philz, or CWM custom recovery for your G2 by using the Simple Tool V3.2 For LG G2. If you don't know what this is, or how to go about installing one, you can read our dedicated Android custom recovery article.
3. Do a full reset of your G2, including wiping your internal storage.
4. Download the OptimusG3 v1.0 custom ROM, load in on the G2, and flash it by pointing the custom recovery of choice you loaded in step 2 to the new ROM.
5. If you haven't already, install the latest KK Baseband, too.
6. That's it, you should now have the flat and simple, yet feature-rich G3 interface on your G2, breathing new life in LG's last year finest. This ROM is based on the Korean F400 version, but it's been cleaned up from the Korean carrier apps, bloatware, and deodexed. You also get the LG G3 Camera 4K And 120FPS with Magic Focus, plus more camera tweaks. In addition, there are 13 unlock effects, new themes, ringtones, wallpapers, and notification sounds, so it's actually an improved version of the G3 interface, right on your G2.
source: OptimusRs (XDA-Devs)
Things that are NOT allowed: