Is there a way to change the resolution the game is launched in?

For me, it looks like it's "squished", with a wrong ratio. There's a big bar of nothing at the bottom of the screen. Is there a way to fix this?

Anyone?

Worked perfectly, thanks.

I would also like to thank unifear as this fixed the problem for me as well. Though it's strange because it's worked OK for hours before screwing up the aspect ratio.