Nuendo Expansion Kit upgrading

I have NEK registered in my account but cannot figure out which version it is, probably NEK 4.

How is it possible to upgrade to NEK 5 or 6?

Regards
Denis

AFAIK, if you already own your Nuendo 6 license, you’ll have no other choice than to buy a new NEK 6 license.
http://www.steinberg.net/en/shop/buy_product/product/nuendo-6-expansion-kit.html

Upgrade path is possible for Nuendo or Nuendo+NEK but seems not available for NEK alone.
To be confirmed by Steinberg.