The mainstream operation systems (including mobile OSes) have an upgrade function (in case of a mobile OS, whether your carrier releases updates is a different story….)
Use that function and install those updates!
macOS: Go to the Apple icon, select “About This Mac” and click on “Software Update…” Most of the updates require a reboot, even on MacOS.
Windows: From the “Windows Settings”, go to “Update & Security”. Check for updates, install what’s available and reboot.
Ubuntu: Run ‘sudo apt-get update && apt-get dist-upgrade’
(if you feel like protesting because <your valid reason here>, then you already know what you’re doing and you shouldn’t be reading this anyway (unless you want to fact-check my ramblings))
Other Linux versions use different commands, if you’re unsure, google for the appropriate command on your platform.