Slide the assembly straight back. The front end of the assembly is just held in place with a bracket that it slides into, so pulling straight back will detach the whole assembly, aside from the wires still connected. You can probably get the assembly out with your hands, but it can be difficult to get a good grip on the light to pull it out.  If you can’t get it out, use a flathead screwdriver or other prying device with a rag over the end (to prevent scratching) and gently pop it loose.