Ever since Apple made its Macintosh operating system free, a new version comes out every fall. It’s nice to have a predictable upgrade schedule, but what’s the best way to upgrade Mac OS?

In my experience starting fresh is the best method. I have often seen account folders migrated through four or five Mac computers spanning more than a dozen years. Convenience is the primary motivation when migrating content to a new Mac or when performing an OS upgrade. With this migration or clickable upgrade, unwanted files, incompatible software and obsolete drivers also make their way to the new system. This system junk often takes up valuable space on the hard drive and can lead to confounding software glitches.

To do a clean Mac OS install, you’ll need to have a bootable Mac OS Installer drive. We used to be able to simply pop a Mac OS X DVD Installer into the optical drive, but this is no longer the case. All new Mac OS Installers starting with Mac OS 10.7 Lion have been distributed through the App Store. After downloading the Mac OS Installer app, you can use a tool such as DiskMaker X to create a bootable USB Mac OS Installer onto an 8GB thumb drive.

Upgrade Mac OS with a bootable USB Installer

Prior to formatting your Mac’s internal hard drive for a clean install, you’ll want to make sure to back up all of your data on an external hard drive. This can be done either manually by drag-and-drop or automatically through Time Machine. You’ll need this backup to transfer any documents, pictures, music and files back onto the internal hard drive that has the clean installation of Mac OS.

With a clean installation of Mac OS, you’ll only have the newest system files on your hard drive. It’s as if your Mac was new, similar to the first time you unboxed it and pressed the power button. This method is certainly not as convenient as doing an upgrade through the App Store or using Migration Assistant. Nevertheless the time spent doing a clean install and then manually transferring your files is well worth it. This method guards against many software glitches and also forces you to do the housekeeping necessary to maximize the storage space on your hard drive.