Before you get in over your head.....Get a manual. The Haynes manual covers this fairly well, but not really worth the price. You will need to drill out the pop rivets that locate the regulator to the door frame, and remove the motor and regulator as a unit. It's best to have someone there to hold the glass for you. When you have the regulator and motor assembly out and on the bench, notice that there is a big wound spring that holds tension on the regulator. Be careful of that spring, since there is a lot of energy stored there. There is a hole in the gear plate that will align with a hole in the regulator arm. You will want to take the side plate off the motor and rotate the shaft by hand until these holes align. Put a bolt through the holes, and finger tighten a nut on the bolt to hold things in alignment. Then unbolt the motor from the regulator, and install the new motor. Once you have the new motor bolted to the assembly, you can remove the bolt that you installed through the 2 holes. You did not get your finger cut off either now did you? Installation of the regulator and motor is the reverse of the disassembly. If you don't have the very big pop rivets, and the special pop rivet tool (and it's bigger than the ones that they have at Home Depot) use 1/4" bolts that are 1" long, with lock washers and nuts. They work just fine. Button everything back up, and enjoy your labor.
Those who beat their swords into plowshares, will surely plow for those who did not.