Resetting the display mode

Is there a way to reset the display? I tried to put GTB into a windowed mode and the option buttons are no longer visible at the bottom of the screen, even though I can see the lowest edge of the window it’s in. It doesn’t appear to be resizing.

I did an uninstall/reinstall through steam, and the settings stayed intact, unfortunately.

just delete this file
\my documents\my games\gratuitous tank battles\prefs.ini

Thank you, that got me reset to fullscreen again.

I should note I’m not having a problem using windowed mode when I pick a proper widescreen option. Apparently my choice of a more square option with my drivers fouled things up. I’ve done some massive driver updates and it’s working as expected now.