You should be able to pry off the heatsink w/ little force and twisting motion. But if it's stuck on tight, try the freezer method. Pop the voodoo in a sealed bag, throw it in the freezer for 15min or so, you should then be able to dislodge the heatsink w/ a butter knife.
1.)Insert a razorblade between the heatsink and chip until you get to where the epoxy is, carefully use a sawing motion to remove some of the epoxy to make a nice space to put the screwdriver in.
2.)Use the smallest flathead screwdriver you have (one of those tiny mini ones is best) and turn it using controlled force.
It should pop off easily, then clean up with a little rubbing alcohol, make sure all the remaining epoxy is removed.
I find this method preferable to the freezer method.
Use a pair of needle nose pliers to squeeze the "teeth" of the pins together (back side of the pcb). Once compressed they will push through easily. Don't force anything.
Once the pins are out, the heatsink should come off with minor finger prying. I've done two, one had just silicon thermal grease, one had a sticky thermal pad. Both came off easy, the thermal pad required a bit more torque.