trying to get stuck tire off

Re my original question about a stuck wheel. so many good suggestions. I bought a thing to tighten the valve core before our trip, but couldn't find it when I needed it. I really think the core just needed to be tightened, but decided the tech was a tire expert so went with what he said-
bad mistake. when we get home I'll take rv to someplace so they can do something to loosen
the wheels-i'll suggest some of the things said below. thanks so much. chuck