Observe there are 3 plastic thumbscrews per lamp -- two on top and one at bottom.

Rotate them 1/4 turn (90 degrees) counter-clockwise to unlock.

If they are difficult to turn by hand, a large flat-head screwdriver may also be used.

Once all 3 screws are unlocked, grasp the lamp housing from the rear protrusion, and pull. If you feel a lot of resistance, try wiggling the screws to ensure they have released.

For the plastic thumbscrews, horizontal is locked, vertical is unlocked.

Once the lamp is removed, you can see the three guide pins, which are held by the three thumbscrews.