The upgrade of your PHP-Nuke system to a new version is done in the following steps:
Make a database backup. (See Figure 26-2 and Section 7.1, for PHP-Nuke's own backup function, Section 3.3 for phpMyAdmin's functionality, which also includes a very good web interface to database backups and Section 27.16, for home-made scripts that automate the backup work for you.)
Verify that your current PHP-Nuke version has not been modified (excluding the theme, that does not needs an update). In case it has been modified through the addition of modules that required a change in the original PHP-Nuke files, or the database, proceed manually as outlined in Section 26.3.3.
Test the upgrade locally first and not directly on the production site.
If all looks well, transfer the files and the database to the production site.
The update to a new version itself, is an operation that consists of two parts, the update of the database and the overwriting of the old files with the new ones. The update of the database is done automatically through appropriate scripts that can be found in the upgrades folder of the PHP-Nuke package. You have to upload the right upgrade script to your PHP-Nuke root directory on the server (where also config.php is located), then point your browser to it - this will update the database. See also How to upgrade PHP-Nuke and PHP-Nuke upgrade.
If you are upgrading from a version that is more than one version apart from the version you are aiming at, then you have to apply all patches sequencially, from the old one, through any intermediate versions, up to the newest one. Thus, for the passage of 6.6 to 6.8, you must apply both upgrade66-67.php and upgrade67-68.php.
If you are upgrading from 5.6 to 6.0, you must also overwrite the config.php file with the new one, then edit it again with the right values (see Section 3.7).
The following sections cover some examples in detail.