Back up your Mac with Time Machine or another backup method
Connect your Mac to power
Connect to a stable Wi-Fi network
Click the Apple menu
Open System Settings or System Preferences
Click General
Click Software Update
Wait for your Mac to check for updates
Click Update Now or Upgrade Now if available
Enter your administrator password if prompted
Follow the on-screen instructions
Keep your Mac plugged in during the update
Restart your Mac if prompted
Check Software Update again after installation to confirm it is up to date