Just because your computer’s OS was upgraded doesn’t mean you have to format your mp3 player, but if it is necessary for some other reason there is a Format command in Settings > System Settings (on the player). Note that this will erase all user-added content you have on the device and your personal settings will have to be reset as well.
Also note that Rhapsody will require the device be in MTP mode. This setting is also in Settings > System Settings > USB Mode.
