As far we know it’s not possible to upgrade Fedora 16 to Fedora 20 automatically.
You should backup your NoMachine configuration and restore on newly installed system after updating.
What exactly have to be moved depends on configuration you’re using.
All *.cfg and *.lic files and etc/keys directory are essential and have
to be moved.
Then all *.db files you use, for example users.db if you use User DB, passwords.db if you use Passwords DB and so on.
Steps are written here: