You do not need to edit the cron.php file.
You do have to edit the rcron.php file if you are not using a native task scheduler on the same server as the web site. (rcron stands for remote cron). After you edit it, you have to put it in your osticket tree and call it.
I do not know what Direct admin is, I presume that is some control panel provided by your host.
Either way the cron job needs to run as the user that the website or webserver runs as.
