Ronald Moravec , Apr 13, 2008; 02:39 a.m.
Considering it a plastic lens, be very careful.
Grab in one location with a thumb and one finger and try to turn.
Or put it face down on some rubber or sand paper and turn the lens.
There are filter wrenches that grab all the way around.
In the end, if the rim has been dented and will not turn, then you have to cut it with a Moto tool or other hand grinder. It may reguire more than one cut to accomplish. And do not cut into the lens. Stop short and finish by bending the ring inward. Cut so the debris goes out, not over the glass which needs to be protected in any case.