it tells me 10.4gb will be downloaded ,why that, t's so much
Ever installed Windows ? it requires much more.
Well, You have a new Base, a newer Desktop Environment and all the Software and Packages have to get Updates.
Just also to add; just because it's downloading that much doesn't NECESSARILY mean that that much more disk space is going to be used. It may replace older versions of software, and as such has to redownload the whole thing to set it up again. For example, I have a piece of software that claims it needs "40 GB" when doing an update for it, but in actuality it ends up being the same amount of size on disk, it just downloads a whole 2nd updated version to install, then gets rid of everything it doesn't need.
Applecheeks37 hit the nail on the head.
That is the full size of all the upgrades because they are replacing packages, not being added on top of them.
It would be good if the devs indicated how much spare disk space is needed to operate the upgrader tool. For users of old hardware and limited disk capacity, that may be a problem.
Do the minimum system requirements (disk space) for ZorinOS include for that?
If the upgrader tool is intended to be mainsteam method of doing easy version upgrades, then maybe that should be explained and factored in by the devs who I will tag. @AZorin @zorink
The required disk space is indicated in the Upgrade Zorin OS app, as per the OP's screenshot. When all the system's APT packages are updated, their full .deb files are first downloaded into a temporary directory before being installed. As a result, the system needs at least this much free disk space to proceed with the upgrade. After the upgrade completes, these downloaded .deb packages will get deleted automatically.
If the user previously installed a number of third-party apps or games that take up a lot of disk space, the newer versions of these packages would also be downloaded as such during the upgrade process. This might explain the 10.4 GB download requirement reported by the OP.
In the scenario that the system doesn't have enough free disk space, the Upgrade Zorin OS app will indicate that and prevent you from upgrading to avoid breaking the system.
From that answer, I get the impression you require >50% spare disk space in root to allow upgrader to work.
Not necessarily. I'll give you an example:
If you've installed Zorin OS 16 Core (which takes up just under 15 GB for a stock installation) on a 500 GB drive without installing any additional software afterwards, but filled up the system partition with lots of other data (like 400 GB of documents and photos for example), your disk would be around 83% full.
However, you should still probably be able to upgrade the system to Zorin OS 17 Core, as the proportion of the drive being taken up by software (15 GB or around 3%) is quite small.
It mainly depends on how much software you have installed.