First, Check if your Mac is compatible:
Go to the Apple logo up the top-left (), then click About this Mac.
You'll see some information about your Mac like the below screenshot. Use this information to check that your Mac is compatible by checking off each of the requirements below the screenshot:
1. Check that the version of macOS at the top of the About this Mac window is one of the following: Mavericks, Yosemite, El Capitan, Sierra, High Sierra, or Mojave.
2. Check that your Mac is one from the list of computers below:
- MacBook introduced in 2015 or later
- MacBook Air introduced in 2012 or later
- MacBook Pro introduced in 2012 or later
- Mac mini introduced in 2012 or later
- iMac introduced in 2012 or later
- iMac Pro (all models)
- Mac Pro introduced in 2013 or later
3. Your Mac also needs around ~15GB of storage (check this by clicking on the storage tab of the About this Mac window), and it will need at least 4GB of memory - you can check this in the same place as you checked your macOS version.
If your Mac does not meet any of these requirements, you may not be able to update to the latest version of macOS.
Make a backup
Before installing any upgrade, it’s a good idea to back up your Mac. You can choose to back it up to an external drive, or somewhere like the Google Drive or iCloud Drive.
It takes time to download and install macOS, so make sure that you have a reliable Internet connection. If you're using a Mac notebook computer, plug it into AC power.
Download macOS Catalina
If you're using macOS Mojave, get macOS Catalina via Software Update: Choose Apple menu > System Preferences, then click Software Update.
Or if you're not using macOS Mojave, use this link to open the macOS Catalina page on the App Store: Get macOS Catalina. Then click the Get button or iCloud download icon. If you see the Open button, great! It means you've already downloaded it. Click Open and continue below.
After downloading, the installer opens automatically.
Click Continue and follow the onscreen instructions. You might find it easiest to begin installation in the evening so that it can complete overnight, if needed.
If the installer asks for permission to install a helper tool, enter the administrator name and password that you use to log in to your Mac, then click Add Helper.
Allow installation to complete
Please allow installation to complete without putting your Mac to sleep or closing its lid. Your Mac might restart, show a progress bar, or show a blank screen several times as it installs both macOS and related updates to your Mac firmware.
Stay up to date
After installing macOS Catalina, you will be notified when updates to macOS Catalina are available. You can also use Software Update to check for updates: Choose Apple menu > System Preferences, then click Software Update.
Or get macOS Catalina automatically
If you're using OS X El Capitan v10.11.5 or later and your App Store preferences or Software Update preferences are set to download new updates when available, macOS Catalina will download conveniently in the background, making it even easier to upgrade. A notification will inform you when macOS Catalina is ready to be installed. Click Install to get started, or dismiss the notification to install later. When you're ready to install, just open the file named Install macOS Catalina from your Applications folder.