The extrusion head fan keeps the assembly piece cool and free of debris for continued printing. Before starting this replacement you will need to remove the plastic cover. You will need a hex wrench and a small Phillip's head screwdriver. Be sure you are careful when removing the fan, because it is a thin plastic that is easily breakable.
Remove the plastic cover that sits on the extruder, next to the fan, by lifting the latches in the back. The latches should lift right out.
Using the Phillips #0 screwdriver, locate and remove the two 3mm screws on the top of the fan using a counter-clockwise rotation.
Locate the fan connector, a 2-pin JST type, from the extruder board on the top of the extruder assembly and while firmly holding the plastic part of the connector, wiggle out the wire.
Gently lift the fan off and away from the module. The fan should easily fall out.
Place the replacement fan on the extruder assembly in the right orientation.
Connect the cable make sure that it has a solid connection.
Secure the fan by screwing the top screws back into place in a clockwise rotation.