You can install PHP-Nuke through the automatic script installation system - Fantastico and following these steps:

1. Log in cPanel and go to Fantastico;

2. From Content Management --> PHP-Nuke choose "New Installation";

You can also install Php-Nuke manually. For this purpose follow these instructions:

https://www.siteground.com/tutorials/phpnuke/phpnuke-manual-installation.htm