The following guides show how to remove and replace the rear wheel of your bicycle:
* [guide|4079|Rear Wheel Replacement]
* [guide|31826|Trek 4300 Bicycle Rear Wheel Replacement]
And here are a couple guides to help you fix or replace the rear derailleur on your bicycle:
* [guide|3796|Adjusting the Rear Derailleur]
* [guide|41517|How to adjust Rear Derailleur Cables]
Though not your exact model, check out this [[Topic:Mt. Fury Roadmaster|device page]] for a Roadmaster bicycle that may be similar to yours. On that page you'll find links to more guides that might come in handy as you repair other components on your bike.
Hope this helps!