Since the HD 6970 and HD 6950 use the same PCB, only the latter is missing a few extra power phases. Still the remaining ones are enough to house the disabled shader modules and the clocks of the HD 6970. It’s a simple BIOS flash to turn your HD 6950 into an HD 6970, but in case your card doesn’t boot up you can use the Safe BIOS switch on your card to flash the primary BIOS back to it’s original state.
The guys over at techPowerUp! posted a detailed article how to unlock the HD 6950, head over there to read detailed instructions and grab all the necessary tools.