I think folk have complained about that. Some write to clear some cache but my advice is to research it or ask the maker. I don't want to steer you wrong.
Simplest idea? Reboot it.
I have tried deleting books from my ereader. It confirms that it has been deleted and it is still showing up. Sometimes I have 2 of the same book. One is sometimes a sample and I can't get rid of it. I have gone into the library and I don't see a button for manage my books or my account. Please help???