also what socket is the cpu?
i'm guessing am2.
if so cwiz is right, there is a small lever that you have to disengage on the side of the hsf. lift it up, pull clip of on THE OTHER SIDE of the cpu. then presto-chango it should lift right off.
make sure you clean the cpu and the hsf with high purity alcohol and coffee filters (no lint).
don't put fingerprints on either, make sure there is no dust/lint on either and DONT SCRATCH THE HSF.
"nagasama no longer drinks tecate, or streaks out of the night for anything, and he has a fine wife so he has no use for your girlfriend...she is safe..."