[Larksong]

I've just started to use Calibre with my Sony Reader. I've tried replacing the generic book covers on some of the book files with images of the real covers, which I've downloaded from the Internet into a file. My Calibre library shows the books with the "new" covers, but when I transfer the books to the Sony Reader, they show up with the cover they had when I downloaded the files. Is there a way that Calibre can change the cover within the book file, or am I out of luck?