1)Downolad ATI Tool.
2)Install ATI Tool
3)Launch ATI Tool
4)Click "Scan for artifacts". This will ensure that your card is stable at its default settings.
5)Click "Find Max Core". Now the program will automatically find your highest Core speed. Wait untill you get errors in the artifact scanning test, you can then click "Abort". Lower the clock values by 5-10MHz, then click "Scan for artifacts". If you get no errors, then everything is OK, repeat the same procedure by clicking "Find max mem" for your memory. If you do get errors, lower the clock speed untill you have none. Leave ATI Tool to run in its Artifact scanning mode for about an hour (more is better), and if there are no errors, you have successfully overclocked your card.