Originally Posted by Stinger
Click on the Kobo drive beside your library in Calibre, and it should show you a list of the books on your device. You can select them there and just press the delete key.
You can also just browse to the Kobo drive using your computer, and manually delete the epub files yourself. (it appears in My Computer just like a thumb drive)
You should be able to manually delete them through ADE, not sure if ADE will delete them automatically from the Kobo, or just give you an access denied message after the loan period... I always strip the DRM.
I think you might also be able to delete ADE books using Calibre. I know the developer mentioned he updated the Kobo driver to list ADE books, but don't know if it can only list them, or delete them too.
I may release a Calibre plugin tonight that is capable of managing the content on the Kobo. It can delete kobo delivered books, pdfs and epubs.
It is experimental though and not for all users (need to be running Linux and capable of backing up the entire device before trying it).