Ford feista zetec 2003.. very simple question?

Hi,
Ok here it is cause I dont honestly know. How do you change the brake light bulb.
It is the model with the long lights that sit in on the outside of the boot.
There are two screws that I can see and undo when the boot is up however the light does not want to come off and so I cant get to the bulbs. I dont want to force it as it may break. Am I doing the right thing? Most cars you can get to the bulbs at the back of the light but no matter what I try I cant find access.. Help please and thanks in advance