Frozen collet nut on Craftsman model 315.175040 router

It is a right-hand thread....heat it with a propane torch and that will loosen the nut

hello there. Buffalonyman is correct that heaat will loosen any nut. However, your first issue is that you are turning the nut tighter, not looser. As you look down upon the bit, the nut loosens counterclockwise. If you are using a tiny wrench, like the one that may have come with your router, you will be much happier with a real open end wrench. If you don't have a set, it is worth the small investment. enjoy. AND go to sears.com and you can download a manual.