Note that the CPU will most likely remain stuck to the underside of the heat sink as it's lifted out. Take care not to damage it.

Lift and remove the heat sink assembly from the logic board.

When reassembling your iMac, remove the CPU from the heat sink and reinstall it separately from the heat sink. This will make sure it's installed correctly and prevent damage.

Follow our thermal paste application guide to reapply the thermal paste to the graphics processor (GPU). You should also replace the heavy thermal compound or apply thermal pads to the VRAM chips.