You would just change your cron job and edit the path to PHP. The standard path on most systems is /usr/bin/php. When a server has multi-PHP, the paths can vary. I'd suggest opening a ticket with Plesk or your server provider if you aren't sure what the path to PHP 7 or PHP 5.6 is. If you're web server is running PHP 7, then you'll want to use the CLI version of PHP 7 also so that it matches your ioncube files.