Use this guide to replace or upgrade your RAM chips.
Lay your iMac front side down on a table with the lower edge facing yourself.
Loosen the single Phillips screw in the center of the access door.
Remove the access door from your iMac.
Use the sharp end of a spudger to pull the black plastic RAM tabs out of the memory bay.
Pull the black plastic RAM tab away from your iMac to eject the RAM chip.
Grab the RAM chip by its edges and pull it straight out of its slot.