Some times those screws can be really hard to get out. Before my house was broken into, I had a real long skinny screwdriver that had been ground to a slight angle. That thing would get anything out. Now days I use a T shaped screwdriver I got at Harbor Freight. You may still have to grind those tips a little to fit the slots. I have also used a little screwdriver tip in a little wrench. If you can hold it in place it has a bit more leverage than the little screwdrivers you usually see.