you should be able to do it in your windows system settings.
with a nvidia card you should have a nvidia link there and with an ati card you should have an ati/catalyst link. just click it and you will have a screen with all possible settings.
if you don't have such a link you have to install the latest drivers for you graphicscard first. goto www.nvidia.com or www.ati.com
furthermore make sure that you have the latest version of directX which is available for your system.