Check that your Mac is compatible with the macOS version you want to install
Back up your Mac with Time Machine or another backup method
Connect your Mac to a power source
Connect to a stable internet connection
Open the Apple menu and go to System Settings
Click General
Click Software Update
Wait for macOS to check for available updates
Click Download and Install if the desired macOS version appears
Enter your administrator password if prompted
Wait for the download to complete
Follow the on-screen installation prompts
Agree to the license terms if prompted
Let your Mac restart and finish installing
Sign in after installation completes
If needed, create a bootable installer from the macOS installer app
Restart your Mac and hold the appropriate key to boot from the installer
Open Disk Utility if you need to erase the drive before installing
Select the target disk and proceed with the installation
Follow the on-screen steps until installation finishes