The Theme switcher is designed for users who wish to change their existing site to a completely new design, carrying all content/plugins and menu structure across from the existing site to a new site.
The Theme Switcher creates a working copy for you so that the live site still functions correctly while allowing you time to work on the new design.
This help video shows how you can use the Theme Switcher to completely change your Theme and retain all of your content.
Using the Theme Switcher
It is important to note that not all themes carry the same structure, and as such it may require moving some items around once the content is carried over to put elements in their ideal positions.
Switching between the working copy and live site
This help video shows you how to switch between your live site and working copy.
Making your working copy live
This help video shows you how to make your working copy live once you have finished with your working copy.