If you didn't change the name on the new creation, then that's probably why it won't let you get it from the Gallery. Try saving the updated creation with something like V2 in the name. Then see if you can download the old version from the Gallery. If you can, then you can remove it from the Gallery and THEN delete it from your Library. Always be sure you've removed a creation from the Gallery before deleting it from the Library if you're going to do an updated version.