In config.php, change wwwroot to https://yourdomain and sslproxy to true (we don't do the sslproxy setting, as we have the certificate on our local server - that way, internal clients hit that first which is faster, but they still get a valid https connection).
https://docs.moodle.org/33/en/Transitioning_to_HTTPS}
has more details
https://docs.moodle.org/33/en/Search_and_replace_tool (updates all your links to https)
