Uhmm ... But I assume that you downloaded XXHighEnd earlier ??
Anyway, you can do that on the "Download Area and Release Notes" board. For the latest version this would be :
http://www.phasure.com/index.php?topic=623.0 and the zip to download is always at the very bottom of such a topic.
In XXHighEnd itself there's an Undemo tab, and in there is a PayPal button. That should do it !
You will receive an email instantly (but finish the few forms that come by after pressing the PayPal button), and that email contains the Activation Code that can be stuffed in the field under the PayPal button.
If you have any problems during the process, please let me know !
Peter