Hey Frank, I'm Tim. Once you get ALL of the screws out, and there are alot, and take the battery out, you should be able to run a small flat edge screw driver around the entire edge and see that it will let you put some pressure and come up 360 degrees, you then start gently prying and lifting, make sure you did not miss any screws, especially in the middle. I assume you are attempting a repair, laptops are not easy to work on, but its very doable.
Once all the screws are gone, the "trick" getting the little plastic teeth around the edge to all disengage, don't worry about breaking any of them, since the screws secure it on tightly.
I read your other post, your replacing the harddrive, so this makes sense, like i said, use a flat head and gently pry and pull it, you will know if there is another anchor point, like a single screw in the middle because just the sides will give.