Currently, the "Direct Upgrade" option is in development and not yet released.
We are aware that there are bad guides on the internet that claim you can Upgrade Zorin OS to the Next release easily. These guides are 100% false and will destroy your Zorin OS build.
We strongly advise that users do not attempt to follow these guides.
I had already reached out to the webpage administrator of one of these sites to ask them to remove the false information. They refused to do so. They know it is false. They want it to remain visible and follow-able. You can reach your own conclusions as to their motives... (Money).
To All Users:
Please DO NOT attempt to Upgrade Release until the ZorinGroup officially release a tool to do so.
Reference: