Why do you want to remove the heatsink in the first place? What make model is the RAM?
Generally from a standard view point you shouldn't remove it, at least not to damage the module. From a heat/temps point of view they don't really help much with heat dissipation (except some make/models). In many brand/models they're just for looks and not really helping with heat. If you look closely inside the metal casing of the spreader/heatsink might not be touching some of the chips directly at all.
If the RAM does not get really hot to touch when under load, there's no OC and overvoltage, there's good air flow inside the case they're OK anyway and you can remove them (even assuming they are tightly touching the chips and actually cooling them) .
Some RAM you can just unscrew the heatsink right off and some of them used to have clips to hold the two sides od the spreader together. The spreaders/heastinks stick to chips with thermal pads or tape adhesives and those are a bit risky to remove. You might rip a chip right off the PCB.
There are a lot of guides online as how to remove spreaders/heatsinks from RAM. If you have no prior experience I'd say do not try to remove them or do it at your own risk. You might damage or destroy the RAM and if you remove them that would probably void the lifetime warranty that many RAM modules come with.