Unroot and downgrade LG G2 Mini

I have a LG G2 Mini device that has been rooted. After root procedure I updated it to Lollipop through FOTA and discovered that the update screwed up my whole device. There is a way to cancel the root and downgrade back to version 4.4.2? I have no problem to wipe the device. All I want is to downgrade back to KitKat as fast as possible...