Always remember your configuration.php file is where all your websites access details are stored. If this is "not" set to 0644 you are leaving a simple security hole in your website.
In order to check and/or change this here is what you must do:
1. Use any method you like to access the root folder on your server. This could be cpanel, ftp client or joomla explorer.
2. Select either properties or change permissions and set the chmod to 0644