Are they stripped or are they some sort of Hex or torque screw? If they are indeed stripped, a tool to take out stripped screws may help, but mice can be tricky to work on. You can try drilling them out, but they are typically drilled into a small plastic tube that if drilled may get thin and just snap off. I recently took mine apart because the scroll wheel was slipping on the plastic wheel. I took it apart and applied rubber cement between the plastic wheel and the rubber wheel it rides on.
Make sure you use the largest screw driver you can to get the right amount of torque if it is a phillips screw. Using a small screw driver can strip it. A larger one might find enough to hang onto in order to get it out. The only way to get the mouse apart is those screw. Any other way would be destructive.