When your pool or spa light fails and you need to replace the bulb, the first question you have to answer is what kind of light do you have. You will need to know the manufacture name, model #, voltage and wattage of your light. This information is generally on a label on the backside of the light fixture. This guide shows you how to get to that information.
Most pool light fixtures are secured to the niche in the pool wall with a single screw at the top of the light. Remove this screw. If the pool light is just below the surface, you may be able to remove the screw by leaning over the pool deck. In this case I had to get in the pool and hold my breath to remove the screw. Wear goggles.