How do I know when to upgrade? And how do I upgrade?
Most users upgrade once a few months. Unless there is new feature you’ve been waiting for, then you can obviously upgrade right away.
Upgrade is the same as if you would be installing software for the first time.
When upgrading on my Mac it does not override the previous version and put the new version in Launchpad what do I need to do?
Follow the Guide on installing or updating for macOS. It is at the bottom of the Guides list on the web page.