Dear a.elghobashy,
you could not upgrade with the same serial number. You need a new serial number for PV*SOL premium 2016. If you have a software maintenance, you got this serial number within the software maintenance in the last days via email. If you don't have a software maintenance please contact our sales team for an offer to upgrade your PV*SOL premium 7.5 to PV*SOL premium 2016.
Kind regards
Marc