Hello Giovanni,
Thanks very much for the previous purchase. There should have been a card in the software box with instructions for activating your licence:
http://www.hauptwerk.com/forms/license-updates/
Please follow the instructions on that page and we can then get your licence activated for you. Please also note that it's important that you only use the 'File | Create a license update request' menu function once (until the resulting update has been sent back to you and applied, since using it a second time after sending us a request file would invalidate the first request file and necessitate repeating the process).
Thanks again.