There are two types of pins in my experience, some that have an expansion on the underside and have to be squeezed to pull out or you push down and pull up. I recommend you pull the motherboard to find out what type instead of wrenching on it without knowing. Once you remove the pins you can generally get it off by pulling and gently twisting if you can. The heatsink compound on these can be brutally strong. Its not the same, but i had an aged server system at work, i ended up tearing the processor from the socket while it was locked down because it was so strongly bonded to the heatsink. The motherboard was junked so it didn't matter, but it took me a large screwdriver to break the seal on the heatsink.