How to upgrade to Zorin OS 16 from 15.3 without reinstall?
Please see here:
ZorinGroup is developing a direct Upgrade Option.
However, it is still in development and not yet released.
There have been some scams on Reddit- promising an easy method- It will not upgrade the system, it will only break it. There are current existing threads from users that tried that...
You wait, or you do a clean install. As @Aravisian noted, Zorin is working on a direct upgrade tool, but it is not ready yet. It will come.
Whatever you do, don't try any of the "do it yourself" upgrade "solutions" that are being posted on Reddit and elsewhere -- they don't work and will almost certainly brick your system.
When Zorin OS 15 was released they says will work a upgrade method to 15 from 12.4 but they didn't announced now
I think Zorin brothers are currently super busy.
As @Aravisian posted above, we just have to be patient. It will come for sure eventually.
This also was later addressed by ZorinGroup - Zorin 15 was heavier in development (In fact, they hired in outside contractors to assist) and Direct Upgrade did not make the cut.
ZorinGroup has stated that the option has the Highest Priority now.
That being said... While I can understand how particularly tricky software installs that took a lot of troubleshooting to work can make anyone hesitant to reinstall the OS... I also understand that assembling an Ikea furniture piece the first time takes four times as long as the second. Practice is all you need, at times. I prefer a Fresh Install. It gets you a clean start, removing clutter and patched issues and takes thirty minutes.
The Ubuntu Direct Upgrade option is messy, takes three and a half or more hours, requires the person installing to remain present to watch for option selections and replaces all your sources. It requires a lot of cleaning up after.
I do not know if ZorinGroups efforts will be different.