Bump up the Core, Shader, and Memory clocks to the desired clocks, and test them by playing a GPU intensive video game and looking out for any artifacts (Wrong colours, black patches, missing objects, etc...).
I suggest you don't bump up the numbers too much (20 at a time), and make sure you OC each of the different clocks individually, not all at once... Since it makes it much more difficult to check which of the values have hit their maximum if you do them at once.
As a last note, be sure to crank up the fan speed... Heat is your enemy. You shouldn't let the card go any higher than 80-90C at most.