If you have any version of Zorin OS (9, 12, 15, 16, etc). Will it automatically upgrade to the latest version? For ex: If you have Zorin OS 16, will it upgrade to the next Zorin OS like if it is called Zorin OS 17? Also, If it does, will the data be erased or saved?
No, it will not.
Zorin OS can accept Point Release Upgrades. For example, upgrading from Zorin OS 15.2 to Zorin OS 15.3
The ZorinGroup is working on a Direct Upgrade feature to allow upgrading to the Next Release but it is not yet released.
This feature will be at user control, not automatic.
How will that be released?
Probably to great fanfare.
The ZorinGroup announces all releases. If there is no announcement, then there is no release. If you are on the Zorin Mailing List, you will receive and email.
So there is not direct upgrade yet, but there will be one in the future?
Please read what @Aravisian wrote.
Great! What is meant by user control?
As he wrote, not automatic.
You would need to manually initiate it; it would not do it on its own.
Which is a good thing; that could be quite a shock.
Though I can imagine some people would want that...