[LazyPup]

Absolutely do not use a torch to apply heat to a PVC plastic fitting or pipe. At a minimum the heat would distort the pipe and in a worse case if the PVC were to catch on fire burning PVC emits extremely toxic fumes.

The chrome plated pipe coming out of the wall may be either brass or PVC but ether way, they are basically the same. Simply a 1/2 diameter male thread on each end.

Inside the wall there should be a 90 deg elbow with little mounting ears on either side that are screwed to a wooden block. The end pointing out has 1/2inch female pipe threads to permit screwing the chrome plated shower arm in.

If you are only changing the shower head, there is no reason to remove the chrome shower arm from the wall.

You will need two pair of channel lock pliers and a rag. Wrap a few turns of the rag around the chrome pipe to protect the chrome finish, then hold the pipe steady with one pair of pliers while unsrewing the shower head with the other. When looking at the shower head from the discharge end, the fitting will have to turn counterclockwise.

Before attaching the new shower head wrap the threads of the shower arm with a few turns of teflon tape to lubricate the threads in case you have to take it apart in future.