To force your site to use SSL/https you should create a .htaccess file inside your site's document root folder or If your site is in a sub folder, create a .htaccess file in the corresponding subfolder. You should be able to create or edit your .htaccess file via FTP or using the File Manager available in your hosting control panel.
The .htaccess file should contain the following:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$
https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]