I don't think you have much choice. Assuming you're talking about the blade retaining bolt, you will have to do whatever is necessary to get it off. The best option is to use a large 6 point socket (the type used with air tools). This will avoid rounding off the corners.
A replacement bolt is a standard service item, and will be available from the same place you would get a replacement blade.
phil_saunders@bigfoot.com
Phil Saunders
June 2008