ATI was bough by AMD a few years ago. They continue devloping the video cards and still use the ATI brand.
Go to:
http://support.amd.com/us/gpudownload/windows/Pages/auto_detect.aspx
Click the "Download" button to get the drivers auto detector. Run it.
It will detect your exact card.
If it's a "legacy" card, you'll be directed to a download page.
Download the drivers package and execute it.
If it's a current card, the autodetect application will display a "Download now" button. Click it to get the appropriate drivers. The install process should start automaticaly as soon as the download is completed, but you may also get an "Install now" button. Click that button if needed.
You'll probably be asked to restart the computer to finish the install process. Do it when asked.
Electro, November 2012