Help! I want to put a hand held shower head on my boys tub and I CANNOT get the old shower head off! I think they must have used some powerful stuff to hold it on. I have tried using two pipe wrenches and twisting in opposite ways, I've tried putting CRC lubricant on the threads, but try as I might I can't get the silly thing off. My husband has put all his strength into it as well. Should I just replace the whole shower arm as well? If so, how do I do that? I can't see the place where the shower arm connects, and I don't have any access to the plumbing behind the wall. Thank you for any advice!

Put a wrench on the chrome shower arm and replace the entire mess. The shower arm screws into a drop eared ell, (see image) located inside the wall.
Don't forget to teflon tape the threads and to give the tape al least 5 wraps.
Good luck, Tom