Changing a headlight bulb in a modern car involves finding the right bulb to fit inside the headlight assembly, gathering reference materials and tools and doing the actual change. In older vehicles, the change may involve replacing the entire headlight, including removal of the headlight frame.
To access the headlight bulb in a newer car, open the hood and find the back of the burnt out headlight. Determine which bulb needs replaced and the type of lamp. Pulling the lamp and taking it to the auto parts store is the easiest way to find the right replacement part. Consult the owner's manual for directions, then replace the bulb.
Replacing a headlight lamp in an older vehicle is usually a bit trickier. Most old headlamps have a frame, which must be removed by unscrewing it from the headlamp bracket. Make sure you don't touch the headlamp adjusting screws.
Disconnect the lamp from the electrical connector on the back, which may be accessed from the front of the vehicle or by opening the hood, depending on make and model. Pull the entire lamp out and take it to the auto parts store, if need be, to find a matching light.
Install the new headlight right side up, and plug it into the electrical connector. Push the headlight back until its in place, then replace the frame. If you accidentally touch the adjustment screws, the lights may need to be professionally adjusted before the vehicle is safe to drive at night.