How to disassembly the top panel for repairing buttons

Hello, one of the buttons (+ volume) doesn't click normally and I would like to disassembly the unit to check if it's just dust or dirt and clean it or try to fix it. Does anyone know how to open the top panel. I saw an "exploded view" of the Soundlink II and seemed easy to remove that part but when I removed the back cover, all the back screws and the side panels the top part didn't seem to move at all.

Thanks in advice