Thank you for your replies.
@Stinger... For the downloaded gutenberg books...I think I did what you suggested but via a slightly different route. I deleted the books from calibre (just from the list of books in my library)... but that didn't take them off the ereader. I am still not very knowledgeable re calibre. However when I plugged in my kobo to my laptop I went to computer > e drive (the plugged in kobo) and then deleted them off the drive and hey presto when I unplugged the kobo and it processed the new info the books had been deleted off the ereader... yay!
With the downloaded public library books... I think when the loan period is up and they are deleted from ADE on my laptop and plug my ereader in to my laptop they will be deleted from the ereader.