In front of the multi-colored bar, you will see the phrase, "X. XX GB." If you don't have at least 8 GB of free space, you should delete some old files.
Before you update Mac OS, don’t forget to: Clean up your Mac This is essential if you want a fast and effortless update, and glitchless work of your new mac OS. To give your Mac a cleanup, you need to get rid of system junk, uninstall extra apps, and clean some old caches.
As you’ve probably noticed by now, the next version of Apple’s desktop operating system, mac OS Sierra, is due to be released in the fall.
Following the annual schedule that Apple has kept to for some time, operating systems for both the Mac and for i OS will make their debuts in the coming weeks.
Before you begin the Lion upgrade process, it's a good idea to back up your existing OS X installation.
You can do this using numerous backup utilities, including Time Machine, Carbon Copy Cloner, and Super Duper.
Also keep in mind the App Store will check for system compatibility, so if you can download it to your system without error, then it should install just fine.
To upgrade to Sierra from, say, Mavericks, you’ll have to consequently upgrade to Yosemite and then to El Capitan first.
Another step to consider is to run a few maintenance routines on your hard drive before installing.
At the very basics, reboot the system into Safe Mode and then use Disk Utility to check the hard drive for errors.
If that sounds like a lot of work, you can get a Mac cleaner like Clean My Mac for the job.
That will give your Mac a basic system cleanup, but Clean My Mac is going to come in handy after the update as well.