Switch Template
You can change the template for your website as often as you’d like. When you do this, the fonts/colors/styles associated with your site will change, but your content will not necessarily change. You may want to change your content a bit to match the default look and feel of a new temmplate, so there are a few options available to you when you click “Switch Template”:
Start a New Sub-Site
If you want to use a new template but keep your current site online while you learn it and experiment with it, choose this option. This will leave your current site intact and allow you to work with a new website in the new template. This is a good way to get a "Fresh Start."
Switch Current Site
This will change your current site to take on the fonts/styles/colors of the new template. It will NOT, however, restructure any of your pages, including the home page.
New Homepage
This is the most popular option. It switches the current site to the fonts/styles/colors of the new template, and also creates a new home page for you in the default style of the new template. Your old home page remains intact under Administration > Home. This way, you can always revert back if desired.