Hi, you should not have to remove fitting to renew lamp(bulb).
If correct bathroom type the front glass is usually held in with a wire circlip around rim, you can see an end of it sticking inwards. squeeze the ends in and remove (glass will come too), then lamp should be reachable.
If still unable to do then grasp both sides of flange and put straight down firmly without jerking and fitting will come down to expose a spring clip each side, squeeze clips against body of fitting and keep pulling, reverse to refit,
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