Moving to the new website builder should not mean rebuilding what already works. The upgrade brings your existing site across and picks up where it left off.
Import What You Already Have
The upgrade dialog imports your current site rather than starting from a blank canvas, so your pages and settings come with you.
Your Colour, Matched
Your existing brand colour is matched to the closest colour in the new theme system, so the imported site looks like your site rather than a default template.
Customers Stay Signed In
Publishing the upgraded site does not sign your customers out, so nobody has to recover an account because you changed your website.