To find out what graphics card you have, if you do not know already, right-click anywhere on your desktop, select Properties, go over to the Settings tab, and look under Display. You should see something akin to "Such-and-such monitor on [ card ]."
Then go over to your card manufacturer's website (
ati.com,
nvidia.com, etc. - use Google if you do not know) and download the latest driver they offer. It's a free update.