How to Upgrade to Catalina

You can go to System Preferences/Software Update to confirm availability. If it returns you are up to date then your Mac can't support Catalina. For desktops late 2012 and on are compatable. I don't know about laptops.

That either means that your computer doesn't support Catalina or it hasn't checked in a while. You can look at an Apple support article to see if your computer is supported. I think its 2015 Macs and later. I'm not sure. You can go to the App Store and then search macOS Catalina. You should be able to download the app called "Install macOS Catalina". Then follow the instructions that the app gives.