Is there a way I can change a B2C to a B2B easily?

PRESSERO > *Pressero FAQs
Unfortunately, you are unable switch the site type.  You can duplicate the site and change the site type in Admin > Sites > Duplicate Site.  
 
Please see this article for more information about what is/is not included in a site duplication:  http://support.aleyant.com/kb/a32/duplicating-sites.aspx