These OS versions can upgrade to Sierra: Disk space: 8 GB of free space on drive.
At the very basics, reboot the system into Safe Mode and then use Disk Utility to check the hard drive for errors.Apple's OS X Mavericks is now available for free from the Mac App Store, and if your system meets its minimum requirements then you might be considering installing it.However, you may be concerned about whether you need to prepare your Mac for the upgrade.Then, there’s Watch unlocking for Mac, there’s one-click Apple Pay, tabs in apps, and cross-device copypasting. So, if you were on the fence about upgrading to Sierra, our advice is yes, do upgrade. If you’re running an OS version like Lion (OS X 10.7), you’re looking into a lot of upgrading before getting Sierra.
To upgrade to Sierra from, say, Mavericks, you’ll have to consequently upgrade to Yosemite and then to El Capitan first.
The first thing to find out is if your Mac can run mac OS Sierra.