It doesn't matter if you want to replace the entire engine or just the casing that is mounted on the engine. 

You need

• Open-end wrench 21 mm
• Allen key 2.5 mm
• Allen key 3 mm
• Phillips
• Optional: spray adhesive or hot glue
• Optional: Thread (2m)

Removing the engine

1. Remove the front few centimeters of the rubber mat on your running board
2. Remove the maintenance flap on the front. To do this, loosen 2 screws at the top and bottom of the running board
   
3. Disconnect the four cables leading to the motor.
   
4. Attach the thread to the motor cable.
5. Remove the engine cover left and right
   
6. Loosen the motor axle and the retaining plates. Be careful not to let the motor fall down, but take it away carefully. 

Now you have removed the motor. By following the steps in reverse, you install a new motor. The thread that you tied to the motor cable serves to pull the cable through the cable channel more easily.