If you dont have a security screwdriver set, and you have the larger ones to open do this with a pen, if the smaller you will have to improvise.
Dead simple, take a pen/plastic, remove the gubbins keep the case, heat it up with a lighter, even a touch of flame, shove it in the hole, give is 30seconds to go cold and harden around the shape of the screw, you now have a screwdriver, unscrew, you get one or 2 screws out of each melt, nice little trick worked a treat