Trouble downloaded and updating software macOS

Did you follow the steps in this article to update macOS?

Update macOS on Mac - Apple Support

If you want to install an oder version of macOS, did you use Safari, to open the link in this article?

How to get old versions of macOS - Apple Support

julliiaa wrote:

I downloaded the new version of macOS but nothing happened and my mac is still on old version?

Does this computer Qualify for this " new version " ?

Computer Qualify for the Monterey upgrade

macOS Big Sur 11 hardware requirements

macOS Catalina 10.15 hardware requirements

macOS Mojave 10.14 hardware requirements

Look & see if you have  Install MacsOS Mojave.app in Applications.