You can get activation info from the Activation Center. The developers have specified on their page the ways to access Activation Center. Once your payment is complete, you will have to log-in to the Activation Center in order to access the serial number to unlock the software.
Quote from the developer:
"Full details on the Activation Center is available from the help file in the game and demos, and is directly linked from the 'Activation Instructions' button from the demo screen."