If only the low-beam is out, you will need to replace the low-beam bulb. It is probably not necessary to replace the entire headlight assembly.
how to replace 2007 Mercedes GL450 Headlight Bulb Low Beam
To change the low beam lights on a 1991 Acura Integra open the hood and prop it open. Find the headlight housing and locate the smaller bulbs. Pull those off and replace them.
A sealed beam headlight is just that. The unit is sealed and you replace the entire light. A composite is made of pieces that's why the name. To replace a composite you put a new blub in the back.
Carry it to dealer who will replace on low beam headlight for $15 +/- dollars in about 5 minutes.
The headlight has two filaments. One for the high beam and one for the low beam. The most likely reason the high beam is out is because the high beam filament is broken. Replace the bulb and it should fix it.
replace the high beam bulb
The Low Beam AND High Beam are in the same bulb. The procedure to change it will be in the owners manual.
replace passenger side low beam headlight
replace the low beam headlight bulb
you will probably have to replace the headlight switch.
If you haven't already, replace the headlight. Chris