How do I change the Screen size on my Xbox 360?!?!?!?

I am using a 60 inch wide screen HD T.V. and I have never had problem with it till now.

When I play the 360 part of the screen gets chopped off, but when I try to Change it using my remote it says ';Not Available';

Please help me!How do I change the Screen size on my Xbox 360?!?!?!?
5th blade SETTINGS

CONSOLE SETTINGS

DISPLAY

1980x1600 or 1340x 1280 ^^

widescreen ^^How do I change the Screen size on my Xbox 360?!?!?!?
well, when you're watchin a movie you can push any button then you get a menu of settings and the settings are wide screen and stuff like that