Schwinn S40 DSX part name

Forget new guide wheels. A new rear derailer is the real fix. You will need to order a new one by the number of gears on the rear gear cluster. How the derailer is mounted, Which way it moves when by the spring direction etc... By the way, get a higher quality one than the one you have got. If you go megawheel on the lower guide wheel; which I recommend, you might need a couple more segments in your chain. Yes, you need a new chain. If you wore out a part on you derailer, your chain is getting old. I recently bought a new rear derailure for my wife's bike for 29 bucks at a much better quality than the old one. It does not have problems of getting between gears, clicking etc... like the old one did new.

I think they are guide wheels.

They are called pulleys. when asking for them at the bike shop make sure to let them know the gearing of bike