Delete unattached files in Omeka.net

We are using Omeka.net to do a catalog of instruments (ihsi.omeka.net), so each item has a number of images attached to it. One item had a monster file attached which filled up our 500MB storage, so it had to go. The problem was that the student group then deleted the ITEM, but not before deleteting the FILE. It seems that the file is still there, as we are still at our maximum storage, but now there is no way to see the file to delete it.

Am I daft or is there no way to see a file list for one’s site on omeka.net (hosted; not a local install) system? Or is there a way to purge any files not attached to an item?

Seems like an obvious thing to be able to do, but I can’t see any way to get to any admin panel at the file level.

Thanks.