You would need to do a mod-rewrite in .htaccess to permanently redirect calls to http to https but are you sure that is what you want to do? What is the reason you want to change your site access to a secure connection?
Here is some info about it:
HTTPS (Hypertext Transfer Protocol over Secure Socket Layer - HTTP over SSL), not to be confused with S-HTTP, was developed by Netscape to provide security over standard page requests.
HTTPS is not a separate protocol, but a combination of the HTTP protocol with the SSL underneath, whereby page requests will be encrypted by the browser and de-encrypted at the server end. Likewise, information sent through the server’s HTTPS layer will also be encrypted.
The Secure Socket Layer lies under the HTTP application layering and thus HTTPS uses a different port (port 443) from the standard HTTP port 80 with TCP/IP. The RC4 stream encryption algorithm features a 40-bit key size providing good encryption for the SSL.
Level of Protection with https
While https is great in theory, the level of protection you can expect will depend on a number of factors. These include, but are not limited to, the implementation by the browser, the integrity of the server/software and the cryptographic algorithms used.
For example, using your credit card over the internet through https is certainly the way to go for peace of mind versus completing transactions over a standard http protocol. However, https and encrypted connections are not foolproof, in that your credit card number is only protected on its journey from your computer to the server. There are absolutely no guarantees that the server itself is fully secure, or indeed, your computer.
HTH
