First things first:
de-energise the system. Put on the required PPE. Cordon off the area if necessary.
1 Removal of the inlay plates (if present)
2 Removing the cover plate
3 Release the chain tension, i.e. slacken the chain
4 Remove the sprocket bolts so that it can rotate freely
5 Undo the screw securing the shaft on the outside of the motor that secures the shaft and, if present, loosen the shell coupling
6 Remove shaft if necessary
7 The motor can now be removed from the flange after all screws have been loosened.
Replace and install the motor following steps 7 - 1 backwards