For Mac OS updating, we go to System preferences..
Then, you see this screen, if there is a notification at software update.
You click on the software update.
Mac OS Catalina is version 10.15 and updates WITHIN Catalina look like 10.15.4, 10.15.5 etc
When you can see an update to MacOS Catalina such as 10.15.6 - 8.25 GB. You can click to ‘Upgrade Now’.
You have to update to the lastest version Mac OS Catalina (Mac OS version name 10.14 is an example of out of date).
However, when you see the new operating system with the name like ‘macOS Saigon 10.16.1’ or ‘macOS Big Sur 11.1.1’ You should not click update until the ICT department has sent an email saying it is safe to do so.