There are two methods which you can utilise to force HTTPS in Joomla - we recommend using the first method and updating it in your Joomla Administration page.
Using Joomla Admin
Step 1 -Login to your Joomla administrator area
Step 2 - Click on Global Configuration
Step 3 - Click on (1) Server, (2) drop down the menu for Force HTTPS, (3) Select Entire Site.
Using File Manager Forcing SSL in Joomla requires editing 2 files. You can do this either using FTP or the cPanel File Manager (click here for a guide on using this tool). Both files are located in the root folder (usually called public_html)
Step 1 - The configuration.php file
Find the line that says $live_site = '';
Between the quotes, add your domain name, including the ssl portion