Hey james, Holger is correct in saying that the whole LCD display must be replaced since the glass cannot be easily removed from the backing. Also, I believe that the new LCD and glass will already be attached together when you purchase the replacement.
A guide for replacing the LCD screen has already been written but will not be visible until iFixit publishes it. It should be viewable sometime in the next two weeks. When it is available, you should be able to find it with this link: [guide|56711]
Good luck!
James