Nearly every man-made object, from shelving units to motherboards in computers, is connected by screws. When the head of a screw becomes stripped from improper installation or wear and tear, it can be very difficult to remove. A few tools used in conjunction will help to remove these stubborn parts.
Isolate the screw as best you can from the rest of the object. For instance, if the screw is stuck in a wooden shelf, remove the shelf from the shelving unit. This will allow you better access to the screw.
Don your protective eyewear and face mask. Using a small metal saw, cut a straight line across the head of the screw, regardless of previous lines or grooves. Insert a flathead screwdriver into the new line and remove the screw. You may need to try a few sizes of screwdriver before you find the correct size.
Use a drill if you are unsuccessful with or unable to get a metal saw. Start with the smallest drill bit possible and make a hole in the middle of the screw's head. Drill holes into the screw's head using progressively larger drill bits, until the head of the screw is completely removed. Use pliers to pull or rotate the screw until it is removed.
Get a screw extractor from a hardware store if the other methods do not work. A screw extractor will enter the hole around the screw in order to properly remove it. If you use a screw extractor, be sure you have the right size extractor and bit for the job. Take one of the screws you successfully removed from the same object to a hardware specialty store and have a professional provide you with the correct sizes for your tools.