Take the screws off the outer cover fo the wet end. That will expose the impeller.
At the other end of the pump is a small metal cap in the middle. Pry that off with a screwdriver. That reveals the shaft of the motor which has a slot in it. This allows you to hold the shaft still with a large screwdriver.
While someone holds the shaft with a big screwdriver, you rotate the impeller counter clockwise to unscrew it off the motor shaft.
In my case the impeller was so caked onto the shaft with rust that we could not loosen it. We broke the impeller and still could not unscrew it. The screwdriver keeps jumping out of the slot in the shaft.
So the next step was to take the shaft out of the motor. On the far end of the motor are 4 small looking bolt heads. Undo those. They go right through the motor into the 4 legs of the wet end.
Stand the motor up with the wet end up. Pull hard to pull the wet end motor cover off the motor and you will then have the wet end and armature of the motor in your hands. Heavy.
Place some wood into a large vice and then grip the big silver part of the armature in the vice. Then unscrew the impeller.