Well... there is little to say here, it suffices to go to a site that holds the files and download them. There is only a small remark to make: if you use Windows
and download a version comprised of a file with the ending tar.gz, do not worry, your Winzip supports it without problems. Once downloaded, extract
it and "throw" all its contents in a folder you created for this purpose and you call "Nuke6" or whatever ( sites from which you can download PHP-Nuke are: phpnuke.org, www.spaghettibrain.com etc.).