There are actually a couple of ways to update drivers.
The first thing you need is the drivers, which you would aquire either on the disc that came with the hardware, or via the manufacturer's web site.
Once you have the drivers, you usually do one of the following:
1 - Double-click a downloaded ".exe" driver installer file to install, or insert the CD that came with the hardware and select the option to install the driver(s).
2 - Use the Device Manager, which I indicated above, and right-click the device and select "Update driver" option. At this point, you are usually asked if you want to allow the wizard to check the internet for a compatible driver (I normally select "No") on this one due to my already having the driver file on hand. The next dialog screen asks you if you want Windows to automatically install the drivers, which you would say "Yes" to if you have the drivers on a CD that came with the hardware. If you have the driver files in a folder on your computer, then you would say "No" to Windows automatically installing the drivers and then on the next dialog screen select the "Include this location in the search" and browse to the folder with the driver(s) in it. Once the selections have been made, you click "Next" and Windows will then install the drivers. Note - you usually need to reboot after installing a video driver. 
