Set your electric drill to the reverse setting and insert the bit into the head of the screw. Slowly back out the screw as far as possible. Avoid a fast drill setting as it may strip the screw.
Squirt a few drops of oil-based penetrating lubricant into the screw hole. Allow the lubricant to settle for 30 minutes.
Heat the screw using the metal tip of an empty hot glue gun. The temperature difference in combination with the lubricant will allow for easy removal.
Grip the head of the warped screw using locking pliers. Using force, move the screw back and forth while pulling outward.
Repeat the above steps for all other warped screws.