Mac OS X 10.9 Mavericks, breaks the tradition, and is available free (subject certain license restrictions) for anyone from 10.6.8 through 10.8.5 as long as they meet the system requirements for 10. Enhancements to the Mac App Store to get your Mac ready to upgrade to Mac OS.
(Note: Snow Leopard will not install on some newer Macs made after mid-2011, but some of these Macs will run Snow Leopard although Snow Leopard will not install - there are ways (by using older Macs) to get Snow Leopard running on some newer Macs without installing. I read the following informations from the apple discussion. Mac OS X 10.6.8 update brings with it a number of general operating system. Make certain that your Mac is compatible with whichever OS you plan to upgrade to.
For Lion (OS 10.7) or Mountain Lion (OS 10.8), you need to go to the online Apple Store to purchase and get info on how to download. From there you should be able to download and upgrade to the most current OS (currently OS 10.9 – Mavericks). Go to the Applications folder and open “App Store”. It’s easy and a good idea to stay updatedDir. If you wish to upgrade FROM Snow Leopard, make sure you are running OS 10.6.8. Mike shows you how to upgrade your Snow Leopard, Lion, Mountain Lion, Mavericks, or Yosemite Mac to El Capitan. Afterwards you can start up from your old OS or Snow Leopard by pressing OPTION key during startup. We use the same Apple ID for things like this.
A software upgrade usually increments the first 'dot' number of a product (for example Mac OS X v10.6, Mac OS X v10.5) a downloadable software update usually increments second 'dot' number (for example, Mac OS X v10.6.8, Mac OS X v10.5.8). That is, I bought Lion and Mountain Lion, and App Store on her machine says they are available for download and installation. Key differences A software update is usually downloadable free of charge a software upgrade usually is not. Alternatively, install Snow Leopard to a empty partition that has been formatted as Mac OS Extended (Journaled) with the GUID option. I think I have finally convinced my wife to update her iMac from 10.6.8. however, I recommend making a complete bootable backup before doing so in case something goes wrong during installation, such as power outage. Many people simply upgrade directly over the old OS installation. After installing, do Software Update (under the Apple Menu) to bring Snow Leopard up to OS 10.6.8. If your Mac does not have an optical drive, the DVD has instructions on doing a remote install from another Mac on the same network. Then purchase the Snow Leopard install DVD from the Apple Store. Apple released Mac OS X 10.6.8 last week with the main focus of adding the necessary enhancements for a smooth upgrade to Lion, Apple’s latest revision to the Mac OS. (If the word “Intel” appears anywhere beside “Processor” you have an Intel-based Mac.) To find out go to Apple Menu and select “About This Mac”. If you wish to upgrade TO Snow Leopard (OS 10.6), make sure you have an Intel-based Mac (Snow Leopard will not run on a PowerPC processor) with at least 1GB of memory and has Mac OS 10.5 or earlier.