You can add the following code to your .htaccess file to force your site from HTTP to HTTPS.
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
If you force your site to HTTPS and you are still not seeing your site to be secure you will want to install and enable the Insecure Content Fixer plugin. For information on how to install this plugin, please see How to Install and Activate the Insecure Content Fixer Plugin