set screen to 1280x1024

CDdude55

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Assuming you're running Windows and assuming you're not talking about a video game, you just right click on your desktop, click "screen resolution" and then click the drop down bar and pick which resolution.
 
Another assuming to the above assuming, we have to assume your monitor can actually run at that resolution. If not, you may be able to set it, but it will look really bad if it shows you an image at all.