What is one method to shut down the APU?

Using the APU start/stop switch is the correct method to shut down the Auxiliary Power Unit (APU). This switch is specifically designed for controlling the operation of the APU, including starting and stopping it safely and effectively. When the APU is no longer needed, engaging this switch ensures that the shutdown procedure is carried out in accordance with the operational protocols, helping to avoid potential damage to the unit or connected systems.

The other options do not serve the purpose of shutting down the APU. Increasing the throttle affects the aircraft's main engines and does not impact the APU directly. Disengaging the autopilot is related to flight control systems rather than the operation of the APU. Turning off all electrical systems could disrupt various aircraft functions and is not a recommended or effective method for safely shutting down the APU.