You can purchase the software using the link posted on the official website. There is a form you need to fills. Then, click the numbers at the top for how many license you want to buy and select the payment method. Depending on the selected method, you will be redirected to secure websites to pay for the application. I believe the software and the license keys, as well as instructions, will be sent to the email specified in the form.
Purchase information: http://www.zarastudio.es/buy.php
