Remove the two screws that secure the motor rotor cover, and then gently remove the cover.

Remove the screw that holds the piece, plastic. Note that to remove it you must carefully remove the small spring that connects it to the transparent support where the scroll wheel rests.

Note the strap that helps the motor head, and the spring of the plastic part.

Disassemble the rotor or motor head by prying very gently with an iFixit Opening Tool or other instrument. Note the position where it was before dismounting, as it has only one position for mounting.