Depending on your laptop configuration, you may need to remove tape or a cover to access the heat sink.

Use a Phillips screwdriver to fully loosen (not remove) the four captive screws securing the heat sink. Loosen the screws in descending order based on the numbers stamped next to each screw.

During reassembly, tighten the heat sink screws a few turns at a time in ascending order based on the numbers stamped next to each screw, until snug. This will usually be in an "X" pattern.