I can't speak from personal experience, but as nobody who can do so has, I'll give you as much information as I can. There is a hidden menu which should give you the options you need. To access it hit Menu, then Setup (the option with a satellite dish icon), then cursor right. Press Red, Greeen, Yellow and Blue in that order, then Green Yellow Blue.
This brings up the Manual Setup menu. Click on the first item in this, Antenna Setting to bring up a menu which should give you all the options you need - from there you are on your own unless someone else can talk from experience.