WARNING!!! If you use WORDPRESS or other CMS or Software - you may need to make the https changes inside your administration area of that software!
Add the following to your .htaccess file
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
Your .htaccess file belongs inside your public_html folder
and it is a "HIDDEN FILE" (starts with a .) AND sometimes your ftp/file manager "SETTINGS" will be set to NOT SHOW HIDDEN FILES...
SO, you MAY need to edit your FTP program to show Hidden Files... IN cPanel FILE MANAGER, click on "Settings" BUTTON in UPPER RIGHT HAND CORNER and SELECT "show hidden files".
As always - let us know if you have any questions :)