You will need to follow some special instructions if you are upgrading from an older, 2.x version of Parallels Desktop:

• Enter your 2.x license key here and click on Upgrade. This will take you to the purchase cart.
• After your transaction, download Parallels from the link that is sent to you in your confirmation email.
• Enter the license key that is supplied with the email once prompted to do so.
• Once you start Parallels Desktop 5 for Mac, import your virtual machine by following the instructions on the screen.