Changing from old SiteBuilder to upgraded WebsiteBuilder

If I decide to use the updated Website Builder in building another website besides my current website. How does that work-using the same domain? I created my current site thru "intuit" in yr. 2012. (subsequently, "Homestead") I want to keep content and features I have now the same. Is that possible? Two more questions: Does doing so change the current one? And also, does the charge go up for the upgrade? ( I've used the desktop all along.)