Use a Phillips screwdriver to remove the 11 screws securing the heatsink:

Eight 6.7 mm‑long screws

One 4.6 mm‑long screw

One 5.7 mm‑long screw

One 4 mm‑long screw

This screw may be covered by a sticker. Pierce through it with your screwdriver or use tweezers to remove it.