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"Typically" (deliberately in quotes - ASS U ME its the same as mine), it's the white outer ring you need to remove, i.e. the whole thing. This will be clamped onto the ceiling board via a pivoted spring jobbie (probably has a proper name. Try gently levering the white outer ring away from the ceiling and if it's the same design I'm thinking off it should just pull off. Get it half way and you should be able to see the mechanism and how it works - difficult to describe, but I found a pic:
Once you've got access to it, if it's similar to the above you'll see there's a circlip that holds things together.
Once it's off you should be able to see how to remove the bulb - sometimes the wiring is plugged in from the back and the plug needs removing before the bulb is released.
If it's not that sort of mechanism, then it's likely the bulb will be push up and twist - you might want to try that first. Not dissimilar to a normal light bulb and socket, but the fixing mechanism is on the bottom of the lamp integrated with the contacts rather than being on the side:
Here's a link to a pic
Yep - that's it, just pinch together the two prongs of the retaining circlip with needle nosed pliers (all guitarists should have those for re-stringing) and the whole bulb and socket assembly drops down enough to hold the socket while you twist the bulb out!
I guarantee that when you do it the circlip will flirt across the room - always does, sod's law!
If you dispense with the pliers the sharp tip of the circlip will draw blood on the ball of your thumb - and that's playing the guitar ruled out for a day or so!