IPad- How to return an ebook on Digital Editions

Ah so frustrated! My dad has DAE and has downloaded his maximum 10 ebooks from his library- he has read them ahead of time (before they expire) and wants to return them to free up the licences to borrow more- how the hell do i do that using an ipad? the only option i can see is the bin to delete the files, but this isnt releasing the licences with the library who say the books have to be returned?

just spent the most annoying half hour trying to get any sense out of an online chat convo with adobe who's only solution was to refer me here! 

Can anyone help please?