With the glass up,you undo the three 10mm nuts on the door that hold the motor is place,undo the wires for the motor from the screw terminal block. Don't lose the screws because they are very hard to find. wriggle the motor so the glass drops slightly. Reach up in the door until you can feel the bottom of the glass. there is an arm that connects the motor nit to the glass,on the glass end is a clip which is on the inside of the mechanism. you have to lift this clip up to free the arm from the motors arm. Once it is free,remove the motor and arm as a unit. there are two types of motor unit,a three wire unit and a two wire unit. you can still buy the two wire units new from mercedes but the three wire unit is obsolete and to fit a two wire motor you need to fit a couple of relays to actuate the motor.