I removed mine by placing it in a plastic ziplock, putting it in the freezer for about 30 minutes, then taking a very thin piece of cardbhoard and putting it over the card. Use a butterknife to get between the heatsink and card that is covered by the cardboard and gently twist-pry that heatsink off. It should just pop off.
Doesn't take much force at all and isn't as scary as it sounds. Just be careful about the small transistors on the card...but that is what the cardboard is for.