Which of the following should be done if a hand brake is difficult to release?

If a hand brake is difficult to release, the appropriate action is to charge the air brake system and apply a full service application. This process aids in relieving the pressure on the hand brake mechanism. When the air brake system is charged properly, it can create sufficient pressure that helps to overcome any resistance in the hand brake, making it easier to release. It's a method based on the principles of pneumatic systems, where increasing air pressure can facilitate movement and release of mechanical components that may be jammed or stuck.

Choosing to move the car without releasing the hand brake is risky and can lead to further complications, damage, or safety hazards. Leaving the car untouched might be an approach if there's a major issue, but it doesn't solve the immediate need to release the hand brake for operations. Increasing the speed to release tension is not a recognized safe practice in railway operations; it can cause accidents and does not address the underlying mechanical difficulty with the hand brake itself. Thus, applying a service application after charging the air system is the best solution to ensure safety and proper functionality.