How can I upgrade from Pro Tools 12 to Pro Tools HD 12

As I mentioned I have Pro Tools 12 running on a Windows 8.1 PC and I have Mbox pro (3rd gen). But from now I want to upgrade that version of Pro Tools into HD 12 version because it can help me a lot with video in the session. So how can I upgrade that? Do I have to buy a new one or there is other way?

Thanks so much!
Best regards