Updating an old os
If you can't see the version of OS X you want in your Purchased list, you've probably not downloaded it, or it may never have been available on the Mac App Store.
The one thing you really mustn't do is go to a torrent site and download a copy of the OS X you want.
If it’s OS X 10.8 Mountain Lion that you need you can buy it for £19.99 here.
As with Lion, Apple will send you a download code to use on the Mac App Store, so you will need to be running Snow Leopard to install it.
Note: You won't be able to simply install an older version of the operating system directly onto a machine running a newer version of OS X or mac OS.
However, it can be used to upgrade a Mac running an earlier operating system, or you can follow some of the advice below to install the older version on your Mac alongside the current version of mac OS.
Perhaps you are relying on software you have discovered doesn't work properly in the newest version.
Blizzard titles require version 10.9.5 or newer to run properly.Out-of-date drivers and operating systems can cause a variety of issues and are one of the first things to check when a game is having problems.The instructions below will help you check and update your drivers.The other possibility is that you downloaded it while logged in to another Apple ID - if you think that might be the case, log in using that ID.
Alternatively, find someone who has downloaded that version of the Mac operating system and ask them to download the installation file for you.
In the case of Snow Leopard you will be sent a physical box containing an optical disc - so you will need a CD/DVD drive to install it.