Insert the blade of the slotted screwdriver into the slot of the screw if there is paint around the flat head screw. Gently tap the bottom of the screwdriver with the hammer to remove any dried paint from the slot of the screw to allow the blade of the screwdriver to fit into the screw properly.
Insert the proper screwdriver into the slot of the screw. If the screw is one slot, use the slotted screwdriver. If the screw has a cross head slot, use the screwdriver with the cross head blade.
Begin to turn the screwdriver to the left to loosen the screw. If, after exerting a reasonable amount of force on the screwdriver to loosen the screw, the screw will not move, stop trying for a moment. If you continue to try to force the screw to move when it is stuck, you risk stripping the screw and making it very difficult to remove.
Place the wrench around the shank of the screwdriver and tighten the wrench snugly. Press the palm of your hand down firmly on the top of the screwdriver and turn the wrench to the left at the same time. The additional leverage of the wrench should be enough to loosen the stuck screw.
Remove the wrench from the screwdriver after you have loosened the screw slightly. Continue turning the screwdriver to the left to remove the screw completely.