Turn off your pressure washer. Use a wrench to remove all bolts holding the pressure washer cover to the frame of the unit.
Remove the cover of the pressure washer to expose the internal components.
Locate the pump assembly on the inside of the unit. It is a cluster of metal valves with various hoses connected to the ends of the valves.
Unplug the hoses from the valve ends.
Remove the mounting bolts holding the pump assembly in place.
Remove the pump assembly. You can now fit a new pump assembly in the old one's place.