Plumbing problem - fitting stuck? I'm trying to change the cartridges on the tap, but I can't...

I'm trying to change the cartridges on the tap, but I can't remove them. I just terminate up stripping the fitting trying to take them out. What can I do to remove them? The corners on the fitting are already pretty rounded from my previous attempts
Answers:    involve to know the make of the faucet . near are several types and the way they come apart is different. also a pic would be terrifically beneficial if possible.
Try a mixing bowl wrench or 14" pair of Channel locks. They both own teeth that can bite into the brass. Then squeese hard and turn slowly. If you are not strong next find someone who can squeese them babie hard and turn them out.