Usually, stripped screws can be removed using a small flat blade screwdriver (like what is used to repair eyeglasses or other smaller objects) Just be sure to use a Flat screwdriver (-), not a Philips screwdriver (x). The screwdriver blade should be as wide as one part that makes up the Phillips (x). While pushing straight down onto the screw head, slowly turn it counterclockwise to loosen the screw.
Or, sometimes, a rubber band that is as wide as the screw head will do the trick. Place part of the rubber band flat over the head of the screwhead. Insert your Phillips screwdriver (x) into the rubber band. Turn the screwdriver counterclockwise to remove the stripped screw.
Once the stripped screw is removed, replace it with a new one of the same size and shape. Then when the screw needs to be loosened in the future, use a Philips screwdriver that is not too large for size of the screw. Otherwise, it may become stripped, too.