Final answer:
A train operator should wait for the signal to turn green before proceeding when stopped at a home signal indicating STOP on an upgrade.
Step-by-step explanation:
When a train operator stops at a home signal indicating STOP and the train is on an upgrade, the correct action for the train operator to take is to wait for the signal to turn green. Continuing to drive the train, reversing the train, or changing tracks are not appropriate actions when faced with a stop signal.
The operator should ensure the train remains stationary until the signal indicates it is safe to proceed. This protocol is similar to road vehicle drivers who must stop at a red traffic light; they should only proceed when the light turns green unless there are extreme circumstances, such as transporting someone who needs urgent medical assistance.