Hello Deltahost,
You can update your existing CCv3 installations with the new keys by editing /usr/local/centovacast/etc/license.conf, replacing the key there, and then restarting Centova Cast (/etc/init.d/centovacast restart).
Delete the current license information already stored on your server by running the following command:
rm -f /usr/local/centovacast/etc/license/license.key
Now just restart Centova Cast:
/etc/init.d/centovacast restart
or
service centovacast restart
And finally, use the following command to update the web interface as well:
/usr/local/centovacast/bin/ccmanage cronjob --job=pollhosts --force
If you don't see any error messages, then you have successfully installed your new license key.
Just make sure to re-issue your license before, and that you're not using it already on another installation.