You can install them following the instructions found here
Read the guide carefully, and it will go OK.
If anything breaks, most possibly you will not get any graphics, be sure to write down the necessary commands to return to the original state. Just hit
F1 to switch to a command line and enter the commands.
It has happened to me before, but removing the drivers and returning to the open source ones fixed it. However, generally the proprietary drivers are faster and support better 3d performance.
The GUI installer found on ATI site never worked for me so I do not recommend it. The above method worked every time.