Turn off the electric to the pump.
Drain the pump by removing the two drain plugs on the bottom front and the bottom side underneath the pump.
Disconnect the electrical cord from the wall outlet and from the pump itself. Unscrew the plate on the back of the pump after you pull the plug out of the wall outlet. The other end of the cord is connected to the pump with slip connectors which pull off or screws; use the screwdriver in the latter case.
Remove the pump from the pipes connecting it to the filter. The pump is connected to the plumbing in two places: on the suction side of the pump and on the discharge side. If the pump is connected with unions use a pair of channel locks to unscrew the unions counterclockwise to loosen them.
If there are no unions, cut the pipe with a PVC saw in order to remove the pump. (If the pipe is cut it will have to be glued back together with PVC cement and a couple of couplings.)
Remove any remaining fittings on the pump housing by turning them counterclockwise. Set the new pump in place and install it by reversing the procedure that was used to remove the old pump.
Use Teflon tape on all fittings before reinstalling them. Replace the electrical cord if it looks to be worn or frayed.