To remove the power supply unit, identify and unlatch the base cover to remove it. Then unlatch and remove the front bezel. Find and unlatch the hard drive from the system. Identify the power supply unit and disconnect the cables. Remove the 3 screws and unlatch the unit to remove.
To reinstall the power supply unit, relatch it to the system, tighten the 3 screws and reconnect the cables. Relatch the hard drive to the system. Place the front bezel and base cover back on the system.