iFixit

If your mini has neither an Airport card nor a Bluetooth board, you can simply lift the optical drive up and away. Otherwise, you need to disconnect the Airport and/or Bluetooth antenna cables first.

With your free hand, pull the Bluetooth cable up from Bluetooth board and unplug the Airport antenna cable from the right of the Airport card. Caution: both of these connections are very small. When re-assembling unit after repair, you may want to remove the two screws holding the airport card to the assembly and lift the card up and out to re-attach the cables.

Flip the mass storage assembly over so that the fan faces up.

Remove the three long, black Phillips screws from the corners of the fan. These screws are strongly threaded, and will offer significant resistance.

There is no screw in the bottom left corner.

Lift the fan up and deroute its cable from the plastic framework and the bottom of the hard drive, removing tape as necessary.

The cable you're about to remove is very fragile - do not pull directly on the wires. Instead, try to pry up the connector directly, using your fingernails or a small flathead screwdriver if necessary.

Disconnect the fan connector from the interface board.