How to Find Your OS X Version Number Click the Apple icon at the top left of your screen. Choose the first item in the menu, “About This Mac.” Take note of your Mac operating system, both by its codename and its version number. For instance, this is v10.10.5, also known as Yosemite.Which version of Mac OS X do I have?
Which macOS version is installed? From the Apple menu in the corner of your screen, choose About This Mac . You should see the macOS name, such as macOS Big Sur , followed by its version number. If you need to know the build number as well, click the version number to see it.How do you install Mac OS X?
Start the installation from a working computer. If your computer can boot into OS X, you can start the installation process from within the operating system. Insert the installation DVD into your computer, and wait for it to appear on your desktop. Double-click the "Install Mac OS X" icon, and then click Restart.Can I get old versions of Mac OS X?
You can see all previous versions of OS X your Mac has installed by opening up the App Store and clicking the icon in Applications. Tab to the Purchase page of the menu and scroll down to find the line for previous operating systems . Clicking the install button of the macOS you want will begin downloading the file.