The Toyota Previa uses a composite headlight assembly and a set of halogen headlight bulbs. Under normal circumstances, you would not need to remove the entire headlight assembly unless it is broken or otherwise damaged. The bulbs can be removed from the back side of the assembly with little effort. If the entire assembly requires replacement, a new assembly is available from a Toyota dealership or some auto-parts stores that specialise in crash parts.
Open the hood of your Previa and locate the headlight assembly. Look for the bulb in the rear of the assembly, then reach in and remove the electrical connector from the headlight after releasing the locking tab on the connector.
Lay the wiring harness and connector aside and rotate the locking ring on the bulb counterclockwise. Pull the bulb straight out of the assembly and set it aside. Do not touch the glass section of the bulb or you will damage it. The oil on your hands will weaken the glass and cause it to fail.
Locate the two aiming nuts on the shafts on either side of the bulb socket. Remove the two nuts with a deep socket and ratchet, then unclasp the aiming spring at the bottom inside edge of the assembly.
Pull the entire assembly out the front of the van and set it aside. Repeat the process to remove the assembly on the opposite side of the van.