You're going to be making major changes to your Mac: installing new system files, deleting old ones, applying for new permissions, and resetting preferences.
OS X Mavericks (version 10.9) is the tenth major release of OS X (now named mac OS), Apple Inc.'s desktop and server operating system for Macintosh computers.
To put it simply, if your Mac can run OS X Mavericks, it should have no difficulty with OS X Yosemite.
You can find a detailed list of which Macs will be supported in the guide: OS X Yosemite Minimum Requirements Once you're sure that your Mac meets the minimum requirements, you're almost ready to proceed, but there are still a few more steps to go through to ensure that your expectations will be met by Yosemite.
During a keynote on October 22, 2013, Apple announced that the official release of 10.9 on the Mac App Store would be available immediately, and that unlike previous versions of OS X, 10.9 would be available at no charge to all users running Snow Leopard (10.6.8) or later.
This is to increase performance and cross-platform compatibility.
Really, it's hard to go wrong with this simple installation method.It also tells you how to work out what is the newest version of OSX that you can run on your computer.Some older Macintosh computers won’t run the latest version of OS X.Some skeuomorphs, such as the leather texture in Calendar, the legal pad theme of Notes, and the book-like appearance of Contacts, have been removed from the UI.Pinch-to-zoom and swipe-to-navigate-history gestures have been removed, although both are supported anywhere else.