If the monitor and the videocard do support this resolution it's just a setting in the display properties. Right click on an empty part of the desktop, choose properties, locate the resolution slider and drag it a little bit to the right.
If your videocard supports this resolution, but your monitor doesn't either the possibility isn't offered by the slider or you get a horrible display. Don't accept the new setting then, and keep the old setting. Then go and buy a new monitor.
If your video doesn't support this resolution, buy a new videocard and install it. You might have to disable any onboard video in the BIOS.
Kees