How do you replace a light bulb on a headlight?
Most of the newer bulbs can be removed by turning them counterclockwise after first removing the electrical connection. Purchase the replacement bulb first and have a look at the way it connects to the wiring and how it attaches to the headlight assembly. After sitting there for a few years the rubber often gets a little hard and is usually stuck to the headlight assembly so it might take a little effort. Hopefully removing it doesn't damage the assembly.