first rule     : You cannot remove white alu heatsinks with black bonding adhesive from like B2 4,66th machine.
second rule : You cannot remove otherside of pcb brown chromium plated heatsinks, these are soldered.
                    (i replated these with Boron Nitride because they have different voltages and high conductive,
                      when white heatsinks dropped on these BOOOM SHORT CIRCUIT !)
third rule    : Do NOT USE BRUTE FORCE

now, 3 main rules for happy faces
-inspect pcb and be sure its a white glue between heatsink and chip
-set your "smd heat gun" (not heatgun) to 220 C
-cover thin flat watchmaker screw driver with kapton tape (for nice force)
-put screwdriver between heatsink and pcb and dont push
-put smdhg to top of the heatsink and wait 15sec.
-slowly push and check heatsink and make a little angle difference
finally some ones easyly drops...
-find a metal bath, fill with cellulosic thinner
-immerse pcb in it and use brush for remove white al2o3 particles
-you can use plastic thing to remove hardest epoxy on center of chip. (center is very hard to remove)
finally you can use F800 sandpaper for polish heatsinks
i said again, if you dont have electronic skills DONT DO THAT. because maybe you can broke chip solderings...