To replace the motors you will need the following tools:

Wrench 10 mm

allen key 2

allen key 2.5

1. Please disconnect the printer from the power source.

2. Remove the x-motors connector of the motor you would like to replace. Please see the picture below.
When removing the connector, please avoid pulling wires. Instead pull the connector. 

3. Loose the nut in the picture below to be able to remove the timing belt. Use Wrench 10 mm:

4. Remove  the black grub screws to be able to pull of the timing belt gear and attach it to the replacement motor. Use allen key 2.

4. Then remove the marked  screws with a number 2.5 allen key and switch the damaged motor with a new one 

5. Now fasten the timing belt and  put back the x-motor connector.