Firstly check out the hex driver. More often it is a worn tool that damages heads rather than the screws being worn themselves. (A reason to always use good tools)
As for options, they are limited. Try a new tool or allen key is always a good start. Secondly, one of my favourite tricks is using imperial tools. I've pinch a handful of my dads imperial allen keys, and you can often find ones what are ever so slightly larger than the proper metric tool, jam it into the head and then unscrew it. The next option is creating a flat section across the head of the screw and then using a flat head screwdriver to undo it. If the head is exposed (like a cap or button head) a saw will do this. If it's countersunk it's a little more difficult (though totally possible) and usually requires something like a dremel with a small circular plate saw or any other tool that can get into the screw.
The last option, and really last resort is drilling the screws out. Usually a small diameter drill piece will do the trick, and a left hand tap will help in removing them.
Good luck!
