The SMARTEST way to do that is this:
a)
keep your live store running, as-is. With its own admin. Its own database. Its own folder of files on the server. Everything as-is.
b)
build your new store in a temporary location. THIS IS ONLY FOR TESTING AND PREPARING FOR LIVE DEPLOYMENT.
This separate testing area will use a complete copy of your live site, in another subdirectory of your site, AND another database.
This is done following the main upgrade procedure as described in steps a), b), c) above, and in more detail at this FAQ article:
http://www.zen-cart.com/content.php?...-zen-cart-site