In most cars, the headlight bulbs are accessed through a plastic or rubber cover directly behind the headlight housing.
- Disconnect the power cable
- Remove the cover - it may pull of, screw off, or be retained by screws or clips
- Unhook the bulb retaining arm - a shaped bit of wire that holds the bulb firmly in the socket
- Remove the bulb
- Replacement is the reverse. The bulb will generally only fit into the bulb holder one way up, so ensure it is seated properly before hooking the retaining arm back in place.