Use a Phillips screwdriver to remove the six screws securing the heatsink and fan:

Two 5.6 mm‑long screws on the fan

Four 3.7 mm‑long screws on the heatsink

During reassembly, tighten the heatsink screws in an "X" pattern. For example: top left, bottom right, bottom left, top right. This ensures even pressure across the heatsink and CPU.