See - https://www.novell.com/documentation/zenworks-23.4/zen_version_currency_2020_23.4/data/zen_version_currency_2020_23.4.html

Let me "SUMMARIZE" what you are going to do.

By NO MEANS am I going to cover every step....That is what the Docs are for...

You will be importing a new 20.2 Appliance w/o powering it on and then making a COPY of your VAStorage Disk and attaching it to the new Applliance.  When it powers on, it will walk you through the upgrade process.  Once the 20.2 Upgrade is complete you will IMMEDIATELY import the ZCM 23.4 System Update using "ZMAN SUI" to import the update you had downloaded in advance from SLD.  Then apply the ZCM 23.4 SU to your 20.2 Server during the same maintenance Window.

ZCM 20.2 GOLD/Shipping has a number of issues that require immediate patching because ZCM 20.1 to 20.2 despite it's name was a MASSIVE change on the backend.  Perhaps the largest ever....Applying ZCM 23.4 is MUCH simpler and easier than applying all of the needed patches to stabilize ZCM 20.2...which is still out of support.

Once your Primary(Primaries) are at 23.4, you can take a break and go home and let everything running as is for a bit....But don't upgrade your PCs right away if using DLU.  There is one important patch for the 23.4 Agent with DLU we will want to integrate first.  If you are not using DLU there are not any Critical Patches. (There are patches you can apply but not a MUST.)

There are also some Server Side patches I would apply....but again...those are not critical to be applied ASAP as 23.4 is generally stable out the door.

--

ZCM 23.4 is a "Long-Term Release" and will be supported until Late 2026 at the least.  So at this point, you can choose to stick there or go to the latest which is currently ZCM 24.2, but I would hold off on that because ZCM 24.4 is coming out in 1-2 weeks.  The reason I suggest holding off is not due to issues in 24.2, but simply to save the need to do two upgrades instead of one.

The main thing ZCM 24.4 will provide over 23.4 is support for Windows 24H2.  However, I suspect support for 24H2 will flow back to 23.4 in time...but the focus has been on getting that support added to ZCM 24.4 first.  (Note: I have Win11 24H2 on my ZCM 23.4 PCs in my lab and it works great.....It's just a few minor things.)

TIPs...

#1 - If using an eDir User Source...Make sure eDir is at least 9.0.  Edir 8.8 does not support TLS 1.2 and later versions of ZCM drop support for TLS 1.0 since it is no longer secure.

#2 - Make sure your ZCM CA is using a SHA-256 CA Cert.  (If it was creating using ZCM 11.4.0 or later....Unless your CA Cert is about 8-9 years old, you should be safe....ZCM 11.4 was released in July 2015...so the Window where old SHA-1 CAs made by ZCM 11.3 or older is very small.

#3 - Make sure you have plenty of Disk Space...The docs cover that....

#4 - Not a biggy and not official...But if your Primary is still running with the bare minimum of 16GB...I might suggest bumping it to 20GB.  While we don't document needed more RAM....We have more services on the later versions so 16GB is very tight.

Awesome, thanks for all that information. I just wanted to make sure that I needed to follow the migration documentation when upgrading. The people in my position before me had the mindset of if it's not broken then why fix it so this is one of my projects to get updated so we could get off the old 2008 server version. We aren't using eDir and now have our Active Directory forest upgraded to 2019 at the moment and I know that still needs to go up hired, but this was also running on 2008. The current cert we are using is the one that was created internal with the new 20.0 version that was upgraded with update 1. 

Your CA should be great then.  TLS should not be an issue to AD...I've only seen it old eDir 8.8 systems. (EOL Eons ago...part off the don't fix if not broken....)

I was able to create a test envirnoment and ran through the migrateion process and it went smooth, so thanks for the help on that. I tried uploading the ZENworks_23.4_Update.zip to the tmp folder location, but then when I click on start upload, it doesn't do anything and then gives me a red ! with no error or anything. Do you know why this is happening or if there is a log I can look at? 

Are you using the the The Appliance Port 9443 to upload/download files?

If so, use port 9443 to make sure the SSH system service is running...

Then start using 

https://winscp.net/eng/index.php to upload/download files.

It's a GREAT open source project....You will thank me and never want to use Port 9443 to transfer files again.

Then you will also be able to use this to access the Console...

https://putty.org/ and grab Putty.....

The best part of Putty is you can Copy/Paste between your SSH session and Windows. (Right Click to Copy.)

You will never use 9443 to access the console either