To replace you video drivers, you first need to know what video card you have (brand/model). Start DXDIAG (Start->Run->DXDIAG), and after it is finished running (note the progress bar in the lower left corner), select the "Display" tab.
In this panel you will find a description of the sound card in the upper left section. You will also find the driver version number in the upper right section.
Once you have determined the manufacturer, you can go to thier WEB site to get updated video drivers. For NVidia based products it is
http://www.nvidia.com and for ATI products it is
http://www.ati.com.When you get ready to download the driver file, make sure you note where on your hard drive the file will be placed as you will need to reference it in the near future.
Before installing the file you just downloaded, go to the Windows Control Panel (Start->Settings->Control Panel) and invoke the "Add/Remove Programs" ICON. In the list of installed items, find the one that references the video card driver. Uninstall the driver and reboot.
If the driver was successfully removed the screen/display will now look large and ugly. It should be running in SVGA mode (6480x480).
You are now ready to install the new video drivers. Find the file you downloaded and execute it (double-click on it). This will install the new drivers. After the system is rebooted, the screen should return to a somewhat normal look. You can right click anywhere on the desktop and select "Properties" to get the video control panel. There you can make adjustments and verify the driver installation went as expected.
You need to check the monitor display tab to make sure the monitor has been recognized by the new video drivers or you will not be running in optimal mode for the monitor. If the monitor is not properly listed (manufacturer/model), then you need to install the INF files for the monitor. You can also get those from the monitor manufacturer WEB site.
It sounds a bit complicated, and it is. Just take your time.