Turn the power to the pump off through the circuit breaker. 

Separate the pump drive end from the volute or pump housing.  On many pumps this is acomplished through a series of nuts and bolts or by loosening a band clamp that connects the seal plate and volute.  Be careful not to damage the diffuser or impeller contained within.

Turn the motor on it's nose to access the wiring junction box on the back end of the motor.

Remove the dust shield from the wiring junction box carefully.  As a rule, these are secured with machine screws with a 1/4 inch head.  Carefully verify that turning the breaker off turned the power to the motor off with your multimeter.

Remove the wiring from the wiring terminal bar and remove the conduit or strain relief from the motor itself, taking note on if the motor is installed as a high or low voltage installation. 

Disconnect the bare bond wire from the bonding lug.

Take the motor to someplace where you can comfortably work on it.

Laying the motor on it's side remove the diffuser from covering the impeller if it did not come off during the disassembly process.

On the opposite or back end of the motor gain access to the motor shaft.  This may have already been accomplished by accessing the wiring connections, if not there is generally a twist lock cover or friction set cover in the center of the rear housing.

The end of the shaft will typically have double-d flats cut into the shaft for you to use an open end wrench to hold the shaft steady while you work.  If there is a switch on the end of the shaft you can typically feed a 7/16 inch wrench in through the gaps and hold the shaft and not rely on a screwdriver. Otherwise using a large flathead screwdriver you can hold the shaft steady in the slot provided.

Check the center of the impeller for a set screw.  Some pump brands use one others do not.  If there is one in place it will be left handed thread.  This is the time to remove the set screw.

Carefully remove the impeller holding the pump shaft steady.  You may need a strap wrench or a large set of slipp joint pliers however you can place a fairly thin screwdriver into the impeller to gain leverage typically.

Remove the seal plate and motor adapter.  On some pumps like the Pentair Whisperflo this is a single part while on others like the Hayward SuperPump it is two separate parts.

Inspect the individual pump parts for damage. 

Replace the diffuser o-ring.  This simple o-ring can allow water pressure to bleed past and cause you to have a more difficult time priming and reduce overall flow.

Remove the seal from the seal plate and install the matching replacement.  Be careful not to touch or damage the ceramic or carbon portions of the seal.

Remove the other half of the seal from the impeller and install the matching replacement.  Be careful not to touch or damage the ceramic or carbon portions of the seal.

Install the motor adapter and seal plate to the repalcement motor.

Again holding the motor shaft, install the impeller.

Install the diffuser over the impeller.

Tote the newly re-assembled drive assembly back to the pump.

Open the wiring junctin box dust cover and re-install the wiring.  Be certain to match your supply voltage with the motor's internal wiring moving jumpers as required.

Connect the bare bond wire to the bonding lug.

Replace the pump housing gasket.

Re-connect the two sections of pool pump.

Open the pump strainer housing and prime the pump.

Close the strainer housing, re-set the breaker and start the pump.

After the pump primes fully check for leaks and clean up your debris.