What socket is it?
new AMD ones have a lever you flip over to allow easy release of the heatsink.
Older AMD and Intel had a spring clip bar that had a slot for a flat screw driver on one side to push down and out away from the cpu for release.
Google image of what I THINK you have.
Please take care as old cpus did not have any way to prevent you from damaging the core if you are too rough with it.