On my 855 there is a spring with a kink in the wire which is pulled over a mounting post in the engine bay just behind the light unit that holds it tight.
No screws or anything else, just the spring.

Put the key in the ignition to position 0
You pull the spring off the mounting post to release the light unit.
Pull the light unit out
Keeping the electrical connections connected, pull the bulb holder out of the light housing.
Change the bulb
Refit in reverse order.
Push the light unit back in place..the spring goes through a hole into the engine bay, and pull the spring so the kink fits over the mounting post.

Now clean all the grime off your hands.
Just a bit fiddly seeing the actual mounting post with your fingers in the way.