Uh-oh. It looks as though the Amazon associate store interface you're embedding may not fully support viewing via SSL — I'm seeing SSL warnings on https://astore.amazon.com/testamentbooks-20 as well. You will probably need to get in touch with Amazon about this.
As far as redirecting to HTTPS goes, you're correct; that would be done through the Panel. Hit the "Edit" button in the "Web Hosting" column of Manage Domains and edit the domain to be a redirect to the "https" version of itself. Before you do this, though, make sure that the HTTPS ("Secure Hosting") side of the domain is not set to "mirror non-secure settings" — having it mirror the non-secure settings (making it be a redirect… to itself) would create a loop.