I have also had success by putting moderate torque on the screwdriver and then tap the handle above your hand. You don't want to smack it hard or you can damage the screw head, it is the same principle as tapping the screw and then using the driver only this way you are applying moderate torque on the screw at the same time you are giving it a light tap. It is the same principle as using an impact driver, only with a lot more care and tenderness. With a proper fitting driver and common sense approach I have managed to loosen screws without damage to the screw head, but it does take time and patience.