With the Basic Website Wizard plan you can have only a single website. It is defined at the point Website Wizard is enabled for your account.

If you need to create more than one websites under the same web hosting account using Website Wizard you need to upgrade its plan to Professional. The upgrade can be order via your SiteGround customer area -> Order.

Once you have upgraded your Website Wizard to the Professional plan you will be able to create additional websites. You can check the following tutorials for more information how to:

Setup a new website for an Addon Domain via Website Wizard.

Setup a new website for a sub-domain/sub-directory via Website Wizard.

More details on how to create and manage a web site using Website Wizard can be found at:

http://www.siteground.com/tutorials/website_wizard/