Please read www.nch.com.au/software/buyfaq.html#UPGRADE:
Q. What is your upgrade policy?
Your registration and activation code will work on any fix or new version of the software released within 3 months from the date of purchase. Your registration and activation code may work on any fix or new version of the software release within 12 months from the date of purchase unless the new version is a major version change. You will always be entitled to discounted upgrade pricing. Use www.nch.com.au/upgrade to purchase.