Certain instruments, markers and other bulbs can be reached without taking the lens off. In order to change these bulbs, one has to take the socket in hand, twist it in the back and pull out the entire socket-bulb assembly. All you have to do is to remove the bulb and insert a new one, then pop up the socket and re-twist it. Some deeper light bulbs are usually covered by carpet work or other interior trimming. Should it be needed, screw(s) connecting the lens to the attaching screw can be unscrewed and the lens and gasket can be taken off. To remove, depress and twist the lamp counterclockwise to the left. Check whether the socket has any corrosion and clean or replace it. To fix, the retaining pins on the side of the bulb have to be inserted in the socket channels and then push and twist the bulb to the right (clockwise) till it fits. When the socket was taken out of the light housing then you should re fit the socket and the socket and put it in position by twisting it. Otherwise, place the lens and gasket and screw the retaining screw(s) in place.