Just to clarify, NiLuJe is talking about a setting that you use when converting a book to mobi (including if you convert a book from mobi to mobi). If you want to change the metadata (author, title, cover, etc.) on a book you got from amazon, you have to connect your kindle to the computer, in Calibre copy to book to the library, then DELETE THE BOOK FROM YOUR KINDLE. You can then change meta data (you don't need to convert, or re-make a mobi file) and send it to your kindle. You MUST remove it from your kindle after bringing it into Calibre, or else the meta data doesn't seem to get put on to the kindle when you send it to your kindle.