Never pry between the circuit board and heatsink because there's a decent chance a chip will be ripped off and pull copper traces from the circuit board in the process. One person tore off 2 chips while attempting to remove a RAM heatsink. Try cutting through the adhesive with a thin razor blade. There are chemicals that can dissolve the tape adhesive without damaging the circuit board, and one type is automotive body trim and weatherstripping remover, sold by automotive paint suppliers. Heat from a hair dryer can help, but do not use a heat gun unless it's regulated and can maintain a temperature below 70C.