1. Upgrade to V20C first before go further - using LGUP.
2. Setup your device, google acc etc, OR later (it is better to factory resetting the device)
3.
COPY the Genisys mod to
ROOT of your internal storage
4. Turn off your device, go to download mode. (Press Vol Down and Plug to pc)
5. Open LGUP, install/upgrade to V20C again, but read carefully for step 6
6. Start the firmware updater like step 1, BUT when it reaches
9% and the "
COM NO.x" appear in your device lcd,
UNPLUG the cable.
7. re-plug the device to your computer, exit LGUP program. Can you see "COM NO.x" ? If YES, go to step 8, otherwise repeat step 4.
8. and then just do the root tutorial while your device's screen appearing the "COM No.x", it means the COM number for your device in your computer.
tutorial for rooting/inject the img file here :
http://forum.xda-developers.com/showpost.php?p=62075670&postcount=381 (go to
step 6 then
step 8, step 7 was check the COM number, you already have it

)
if it helps, hit THANKS

just ask if you get lost, make sure read before proceed AND backup important files.