Within OS X Utilities, choose Reinstall OS X. Prepare a clean external drive (at least 10 GB of storage).
The following method allows you to download Mac OS X Lion, Mountain Lion, and Mavericks.you have already purchased Mountain Lion on the Mac App store in the past or you have connected to the Mac App Store with a Mac that was originally sold with Mountain Lion as the native OS. You can only legally download mountain lion for free if: - you already have a version of Os X that supports the Mac App Store.If your macOS isn't up to date, you may be able to update to a later version. OS X Mountain Lion brings a lot of great things from iPhone, iPad, and iPod touch to the Mac. OS X Mountain Lion is the ninth major release of Mac Operating System, Apple's desktop and server operating system for Macintosh computers. Is your Mac up to date with the latest version of the Mac operating system (macOS or OS X)? Is it using the version required by some other product that you want to use with your Mac? Which versions are earlier (older) or later (newer, more recent)? To find out, learn which version is installed now.