The showerhead is the easiest. It unscrews. Almost any new one will screw onto the shower arm. I'd use teflon tape though to prevent leaking.
The 'faucet' consists of the trim (what you can see) and the valve/cartridge (what you can't see). The trim should also easily unscrew. You can probably replace it with any trim made by the same manufacturer that fits the valve you have inside.
If you want to change the whole valve - like if you wanted to change your single control one to one that lets you separately adjust pressure and temp, then it could harder. You might be able to just replace the cartridge, which should unscrew out of the exposed valve. In some instances you'll have to also replace the mixing valve that's soldered to the h/c water lines and the shower arm. THAT's a pain bkz you have to remove the tiles and open the wall to be able to work. If your valve is against an inside wall, it's usually easier to go in from the other room (drywall's easier to patch than redoing the tile).