Visit the Parallels Online Store to buy a Parallels Desktop subscription:
Click on Upgrade or New License, depending on whether you have a license for one of the previous versions of Parallels Desktop or not. Visit KB 115399 to find out what type of license you need.
Once you select the necessary edition, click the Buy Now button to proceed to checkout.
Fill in your contact and payment information and complete the process. You will get your activation key shortly after the purchase is completed.