Go to the Celemony.com website and log into Your account. You will see your computer name that has Melodyne installed on it. Click the orange "License Options" button and you will be able to click the "Deactivate" button for the Melodyne version on that computer.
Once deactivated from the Celemony website, uninstall the previous Melodyne from your computer, restart and then and then install the newer version of Melodyne and go through the activation process.