As per the ZorinOS 17 release announcement:
Upgrades from Zorin OS 16 to 17 will be available in the coming weeks. Stay tuned to our newsletter to be the first to know when upgrades are enabled.
This means that you will be able to update, but the official upgrade tools has not yet been released. You can subscribe to the newsletter or check in regularly to know when it's available.
However, this doesn't mean that you will be upgraded to the Pro version ZorinOS 17. As I mentioned earlier, each version of ZorinOS Pro has to be purchased separately. Assuming you do have a Pro purchase, then you will likely be able to upgrade, yes.
Note that you will continue to receive updates for ZorinOS 16 Pro until April 2025, so you don't have to make that decision just yet if you don't want to.
In any case, we'll have more details once the upgrade tool is officially available, so stay tuned for that.