How do you replace a headlight on a 93' 940 Volvo?

Buy a 9004 bulb. Note that it has an "O" ring to seal it in. Don't touch the glass part. Your finger prints will attract dirt and create a hot spot. Look behind the headlight where the wires connect. That is the light socket. There is about a 1 1/2" locking ring that you turn to the right about 10 degrees. You actually turn to the left but you are looking at it backwards. Now just pull the bulb and socket out. It may be tight due to the O ring. Unplug the old bulb. Reverse the process to install.