If your Mac is running macOS High Sierra (10.13), you may not be able to get new versions of certain apps to work. For instance, Lightroom and Photoshop's latest versions might not be compatible, which means you will need to upgrade to a higher version like macOS Mojave (10.14). If you're going to perform an install Mojave, you need to check is your Mac ready for Mojave, backup your important data, and, finally, run installer. So, let's preparing Mac for the upgrade to macOS Mojave. MacOS Mojave compatibility. Before you download macOS Mojave you’ll need to make sure that your system can run it.
To get the latest features and maintain the security, stability, compatibility, and performance of your Mac, it's important to keep your software up to date. Apple recommends that you always use the latest macOS that is compatible with your Mac.
Learn how to upgrade to macOS Big Sur, the latest version of macOS.
The version of macOS that came with your Mac is the earliest version it can use. For example, if your Mac came with macOS Big Sur, it will not accept installation of macOS Catalina or earlier.
If a macOS can't be used on your Mac, the App Store or installer will let you know. For example, it might say that it's not compatible with this device or is too old to be opened on this version of macOS. To confirm compatibility before downloading, check the minimum hardware requirements:
Safari uses these links to find the old installers in the App Store. After downloading from the App Store, the installer opens automatically.
Safari downloads the following older installers as a disk image named InstallOS.dmg or InstallMacOSX.dmg. Open the disk image, then open the .pkg installer inside the disk image. It installs an app named Install [Version Name]. Open that app from your Applications folder to begin installing the operating system.