restore ringtone to nexus 4

[jr2002]

ok, i installed zedge to look for some ringtones and then uninstalled as there was just a lot of stuff i didn't want to sort through.

Now i have a new notification called "cesium" which wasn't there before which seems to overwritten the stock "oxygen" ringtone on my nexus 4. -- they both sound the same.

any ideas how to restore the original "oxygen" ringtone and delete that new "cesium" rington