Login in to the Celemony Website and generate your upgraded download by clicking upgrade.
Once you paste your 2.1 Activation code, and select free upgrade, their server will generate the 4.1 download specifically for you.
Download and install that specific version, it will come with the licence inside the download folder. Once you install it, run it from the desktop. You do that by searching Melodyne in your search and click it, then click activate. it will open a page in Explorer which will ask you to activate and voila, it will be activated.