If you don't have the .pub file that created the site, you need to start all
over again. When you build the site with Publisher and then save it as a
Website it creates the html pages and image pages.  To edit the site you
open the .pub file, do your changes and then save as a website again which
replaces all the html files and images.  Publisher can't change the html and
image files into a .pub file.

Many of us have learned the hard way.