How i can change aspect ratio

[oracus]

I Have a laptop with a screen 15,4" and default resolution 1920 x 1200. When i play games the screen fits and the graphics donts seems well, how i can change the aspect ratio so will appears two black bars left and right in that way so i can change the resolution to 1024 x 768 for example? If enyone knows please let me know..Thanks for your attention.



P.S sorry for my bad english. I hope that you understand

 

[sunsider]

rclick your desktop and choose properties. click on settings and under screen size make your adjustment.

 

[oracus]

i mean changing the aspect ratio

I want to change the aspect ratio, not the resolution...That happen with two black bars left and right, so the screen change to square and not widescreen more.