I've scoured the TOH boards to see if I could get an answer, because quite honestly I was afraid that this may be a stupid question, but here it goes...

I'm doing a budget remodel of my bathroom (1987), and one thing I'd like to do is upgrade the chrome shower hardware. Specifically I'm looking to replace the faucet handle, wall flange, shower head, and stem (not sure if these are the correct terms). Is this something that requires a plumber, or is it just like replacing a shower head (screw off & screw on)? I've also heard of something called replacing the shower valves, which I know can cost $500+. Is this the same thing?