You can easily redirect from HTTP to HTTPS automatically using htaccess.
Note: If using WordPress, there are plugins to force HTTPS that work mush better, so they should be used instead.
Find the file .htaccess in the root of public_html (if one does not exist you can create one) and add the following lines:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R=301,L]
