Somebody put it on there. So, someone (you) can take it off. Hopefully the spring clip is like the one with the retail heatsink. It has a notch meant for the tip of a regular screwdriver.
You won't hurt the mainboard by flexing it to remove the heatsink.
Howto
Use the largest screwdriver you have that will securely fit in the notch on the clamp.
Removal is the exact reverse of the installation.