How do I change brake light bulbs?

Tried to change bulb today. Undone the 3 screws and tried to remove it as it said in the manual but it seemed to still be fixed some how and I bottled it pulling it any harder.
Any ideas people. Basic I know but don't want to fork out for a new unit.
Thanks
 
i was the same but like richandgem said give them a pull and they will come out