When I upload theme to my site and live preview it it looks as if the stylesheet is not working. Is there something I need to reset in the path to make it all happy. I am afraid to turn it on for real in case it breaks my site.

You can safely swap between themes and not fear the site will be broken. You may have to load your widgets back into the sidebars since not all themes use the same sidebars or have the same number of sidebars.