To make your entire website secure, you simply need to change your site url to use HTTPS instead of HTTP. Please read <a href="http://codex.wordpress.org/Changing_The_Site_URL">how to change the site url</a>.
Alternatively, you can use URL Filters in the WordPress HTTPS Settings to secure your entire site by putting just '/' as a filter. This will cause any URL with a forward slash to be secure (all of them).