How do you replace glass bulb in fire sprinklers head?

To replace a glass bulb in a fire sprinkler head, first ensure the system is depressurized and water supply is shut off. Carefully remove the damaged sprinkler head from its fitting, then replace the broken glass bulb with a new one of the same type and rating. Reassemble the sprinkler head, ensuring all components are securely fastened, and then reinstall it. Finally, restore the water supply and check for any leaks before testing the system.