Replacing master page layout for documents

Hi all! I have been making a book, and have been using our standard master page layout. I now have to change the master page layout of the whole book, and I have made a document that uses the new master page layout. I did the typical make new master page layout, gave it a name, and everything seemed normal. I then went to add it to the existing documents but, my new layout is nowhere to be found. How do I add this new layout? I thought I could just change out the current master page layout for the new one. The only changes are the graphics at the top, and some header and footer changes. Body text stays the same. I'm on FM11 by the way.