Stock Android Lolipop for LG-H955 (LG G FLEX 2)

Hey Everyone! I am looking to install stock(Original) Android Lolipop 5.1.1. But don't know how to do that.
The LG OS sucks!
I assume I first have to unlock my bootloader and then root my device. not quite sure which tool will help me do it safely.
Help Anyone?