Although Apple works to make its major software updates go without a hitch, things can still go wrong -- as some users reported with iOS 10 last week. Since a big Apple update can take a few hours to install if everything goes right -- and more hours if something goes wrong -- make sure you are prepared. Sierra arrives September 20 as a free download in the Mac App Store, so now's the time to get ready.

Check your hardware

Sierra will run on Macs going back to 2010 and even a few 2009 models: iMacs and MacBooks from late 2009 and later; and MacBook Airs, the MacBook Pros, Mac Minis, and Mac Pros from 2010 and later. However, Apple says that some Sierra features, such as Handoff or Auto Unlock, will require newer Macs. See Apple's upgrade page for a list of models.

Check your memory and storage

Apple suggests you have at least 8.8GB of free storage space to install the Sierra update. Really, if that's all the free storage you have, you may want to take some time now to clean up your disk.

Apple recommends 2GB of memory minimum. If your Mac has just 2GB of memory, consider adding more, if your Mac's RAM can be upgraded, as memory is affordable.

See details about storage and memory by choosing About This Mac from the Apple menu.

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Which OS you are running?

Apple says that if you are running OS X Lion 10.7.5, you can upgrade directly to Sierra.

Update third-party apps

Check that your third-party apps are current. Click the Updates tab in the Mac App Store to see if anything needs updating. Then after you move to Sierra, check again to see if anything is new.

Know your Apple ID

You need an Apple ID to download Sierra from the Mac App Store. If you don't have one, now's the time to get your own. You may be asked for it during the setup process as well, so keep it nearby.

Back everything up

Because an update can sometimes fail, you want a current backup of the contents of your drive -- including files and photo libraries -- before you move to Sierra.

Time Machine is a painless way to back up your important files. But you have several easy options -- see our Mac backup guide.

Early adopter?

While it's cool to be among the first to run a new OS, it doesn't hurt to wait a day or so to see if the upgrade goes smoothly for others before you jump on.

Clifford Colby follows the Mac and Android markets for Download.com. He's been an editor at Peachpit Press and a handful of now-dead computer magazines, including MacWeek, MacUser, and Corporate Computing.