If you purchased a license for Photomatix Essentials or Photomatix Essentials RE, you can upgrade to Photomatix Pro by paying the price difference between both products.
The price difference is US$60 for Photomatix Essentials and US$20 for Photomatix Essentials RE.
To receive the instructions to purchase the upgrade, please enter the email address you used when you ordered your license:
If you don't have access to the email address you used anymore, please contact the Photomatix Support Team.
If you purchased Photomatix Essentials from the Mac App Store, the above form won't work as we don't have any record from Apple's customers. You would need in this case to email us a proof of purchase from the Mac App Store. You can do this with a screenshot (Command+Shift+3) of your iTunes history showing Photomatix Essentials. Here is a helpful link on this.