That’s easy! (Isn’t there a red button to press that says that? Staples, a US office supply store, has these. Open the Rhapsody client on your PC, plug in the Fuze, and right click on the device in the sources pane on the left.
Select Deauthorize. The Rhapsody Channels function will be dropped from the main menu, and the Account choice will drop from the Settings menu.
The only remaining issue will be those now-orphaned subscription files on the device. You can individually erase them, or simply wipe the slate clean. In the same Rhapsody client, you can select Format, or unplug the device, go to Settings > System Settings > Format > Yes, and all media will be cleared from the device, ready for reloading.