Remove the interior door trim. You should find 3 access holes (about 3/4" diameter) in a triangular pattern somewhere near the lower center of the door. Some models did not have the access holes, and had only dimples in the same location. Behind the holes (or dimples) you will have three 8mm bolt heads. Remove these bolts, and unplug the electrical cable from the motor. Reverse the procedure to install the replacement motor, being careful to fully register the motor into the window mechanism before tightening the bolts.
IF the access holes are only dimples, you will need to drill them out with a 3/4" hole saw.