Once you have activated the free SSL (click
here for the guide) you will also need to update your Wordpress site to work with the certificate. If you want all of the site to be served using https then you will need to login to the /wp-admin backend and then go to Settings > General and update the URL to include https from there.
[b]*** Please note, using the 'Always use https' option on the SSL/TLS page won't work correctly with Wordpress and this will not function as intended with the internal page rewrites of Wordpress. ***