The fan is connected by two or three wires. Label the wire placement on the fan before disconnecting the wires. The wires are connected to the fan with slip-on connectors. Firmly pull the connector off (do not pull on the wire) of the fan's terminal. You may need to use a pair of needle-nose pliers to remove the connectors. Inspect the connectors for corrosion. If the connectors are corroded they should be cleaned or replaced.
Remove the fan blade from the old motor and place it onto the new fan motor. The blade made be held in place with a spring or "C" clip. Use a small slot screwdriver to pry off the clip.
Replace the fan onto the mounting bracket and back into the fan housing. Spin the fan to make certain it can turn freely. Replace the rear freezer panel and plug in the freezer.