It is incredibly difficult for a book which was originally self-published or vanity-published to make the transition to commercial publication.
The main reason for this is that most self- and vanity-published books are just plain bad. But even for the few good ones, there are lots of reasons why it’s very unlikely to happen.
I was going to explain it all here, but the wonderful Lynn Price, editorial director for Behler Publications, has already put it far better than I could. Read her piece, then put your self-published work aside and go and write a better book.