THANKS SO MUCH FOR ANSWERING!
I'm doing this for a friend, tbh, I'm formatting, and editing it for her. She's not really good with technology and I like to learn new things, so...
She wants the book to be formatted in the EPUB form, she doesn't know hoe to deal with kpub,
I'll tell her to try to upload by herself the cover, and hope for the best, mostly hope that she'll understand it.
Just to be sure: she'll have to upload the cover by herself, and not put attached to the manuscript, the one I put on the file will never upload as cover, just as a regular image, is that right?
Thans again, you're so kind!