To do a factory reset to all LG brand sets, you should have a factory remote control [not the remote control supplied with the TV]. You can buy it from authorized service centre for LG. There are two types of reset to TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset).
To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight; will be better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here. Pull up older posts
. Surf the site with patience. http://electronicshelponline.blogspot.com/
Service mode entry, adjust and exit procedure to many popular brand TVs are given. Never forget to exit the service mode, after all adjustments have been done.