Use some isopropyll to remove the old Thermal Grease/Compound from the heat sink.

Apply A little amount of Thermal Compound to the Copper part of the cooling unit in the same positioning as the last. A miniscule amount, just enough to create a tiny layer.

Screw in the Cooling unit/Heat sink. Screw the 2 bottom screws first then the top screw.

Plug the wires from the Cooling Fan back into the Mother Board.

There you have it :) Your new Processor is installed.