Thank you very much for your help, Davidfor.
If I understand you correctly, there is no way to update the ereader directly from Calibre by using the metadata feature. Right?
The way I should proceed is: for a given book,correct the autors and titels in the Library of Calibre, and then send this book to the ereader. Go to the ereader and here I would find the same book twice.And now erase the old book from the ereader. Correct?
MAny thanks again.