How do you remove the light bulb from the underwater light?

You need to remove the screw that holds the light ring and pull the whole light fixture out of the water and up onto the deck. There should be enough wire wrapped around the back of the light to allow this. Remove the lens, replace the bulb, and reinstall the lens with a new gasket, being careful not to get any water inside the fixture. Wrap the excess wire around the back of the light fixture and replace it in the niche, securing it with the screw.

A. I would add: You need to test the GFCI, the wiring of the whole fixture - continuity test. If this is a fairly old fixture - my decision would be to replace the entire assmebly with a new one. If you have no GFCI then would be critical that you add one. And lastly but not least, you should have a pool tech service the light. He will know what to look for and how to correct any situation with your light. If there is something wrong with your light assy. and you do not find it by testing you put yourself and anyone who uses the pool in a great deal of danger if the light should malfunction. The codes specify that anytime you work on a pool light you then need to bring that product to current code. That also includes the main drain grate. Yes if you or a pool tech works on any portion of the pool for repairs the code demands that the main drain be brought to current code requirements. So it is not only a matter of just changing the light bulb and gasket.