“This process will erase whichever OS you’re currently using from your hard drive entirely,” Filipowicz and Gil write. “That means any files, programs, or documents you have will be deleted. To save your files, put them on an external hard drive or a cloud-based program like Dropbox, OneDrive, or iCloud. If you don’t save these important files off your computer, you will lose them.”
“Before you erase your current operating system, download macOS High Sierra from the Mac App Store,” Filipowicz and Gil write. “You’ll need a copy of macOS High Sierra to perform a clean install later on. If you don’t create a bootable drive for macOS High Sierra, you’ll have to install an older Mac operating system first and then upgrade to macOS High Sierra afterward.”
The full how to here.
MacDailyNews Take: It’s always nice to have a fresh Mac performing at its best following a clean install!