To remove the power supply unit, unlatch and remove the base cover. And front bezel of the system. Then flip the front panel over to access the internal components of the system. Identify the power supply unit and disconnect the cables. Remove the 3 screws and unlatch the unit to remove it.
To reinstall the power supply unit, relatch it back to the system and install the 3 screws, reconnect the cables. Flip the front panel over and latch the front bezel and base cover on the system.