The free software upgrade is available for users running OS X 10.6.8 and above. You’ll need to carve out some time for the upgrade, as it is listed at a massive 5.16GB. Also, make sure to backup your Mac before upgrading just to be safe.
Yosemite, also known as OS X 10.10, offers a number of new features, including some tight integration with iOS 8 thanks to Handoff and Continuity.
It also features a flatter, more modern look like what was introduced in iOS 7.