Cant find a way to reset display

When I first loaded up halo 4 it asked me to adjust my display size with the use of both the vertical and horizontal facing arrows, I accidentally made it too large for my screen cutting it off on some parts, now I am having trouble trying to reset it, does anyone have an idea what to do?

Sorry mate, I have no idea. To be honest I’m can’t even remember being asked to adjust my display size :s