You are going to have to remove the two screws that hold the motor in place. Start with the rear truck. Lift the motor off, the rear truck will now be free from the frame, remove the two screws that you see on top of the truck holding a brass plate in place. Now all the internal gearing is exposed, clean out the old lube and put in in fresh lube. With the motor, you can oil the armature bearings and you will see a hole in the top of the motor housing were you can put in fresh oil. When putting the motor back on top of the truck, make sure the gears mesh before tightning down the motor screws. The front truck is a little more involved because of the pick up rollers and front coupler. You should have yourself a Greenberg Repair Manual and you will see exploded diagrams of how everything fits together...
Marty