Don't suppose you could get a picture can you? Should require only a Flathead screwdrive to put on the side thats closest to the PSU. The best way is to completely remove the motherboard and put it in a well lit area and flat surface so you can work on it easier.
Kinda need a picture of atleast the heatsink you got to get a better idea, but if it's stock heatsink then yeah, Flathead screwdriver...side near PSU, push STRAIGHT down on that beeotch and then push the screwdrive away from you which brings the tip and the clip towards you to unlatch from the 3 little hooks.