Welcome to Android Central! If it's a preinstalled app, you can't uninstall it--that's what bloatware is all about. You can probably Disable it by going to the App Manager, selecting the music app, and tapping Disable (or Turn Off). This will at least prevent it from opening into RAM.
It's not unusual for apps to automatically reopen, because the system controls that. Android wants to keep RAM relatively full, so if you manually close an app out of RAM, the system will either open it back up soon after, or open a different app automatically.