The easiest way to back up is using Apple's built-in solution, Time Machine. Before you back up, you might want to free up space by getting rid of old files you never use. Reinstalling macOS will wipe everything on your system, so it's vital that you back up first. Presumably, you've used this computer for some time and have personal data on it. The process may look slightly different on your machine. Note: I performed this process using a mid-2012 MacBook Pro running OS X 10.7 Lion and ended with macOS High Sierra. Whether you're having a major problem and want to start fresh, or plan to sell your Mac and need to reset it, reinstalling macOS is a relatively painless process. While there are less invasive ways to make an old Mac feel like new, reinstalling macOS can prove useful in some cases. Most Windows users reinstall their operating system at some point, but this isn't as common a step for Mac users.
