Flip the mother board, so that the heat sink attachment point is visible.

Remove the four screws that are attaching the heat sink (copper) to the motherboard. Use a phillips head PH0 screwdriver to do this.

Clean the interface between the motherboard and the heat sink.

Attach a new heat sink to the motherboard, make sure to reapply the thermal compound (grey material), lock into place by reattaching screws.