You need to buy 10.6 upgrade from the online Apple Store Mac OS X 10.6 Snow Leopard it costs $19.99. OsX upgrades up to and including Snow Leopard (like all Windows. To install OS X 10.8 Mountain Lion, 10.9 Mavericks (free upgrade, but currently unavailable) or OS X 10.10 Yosemite (currently available free upgrade) you need one of these Macs. Dec 21, 2012 IMHO, upgrading older Intel Mac hardware (Core Solo/Duo- and Core 2 Duo-based Macs) to Snow Leopard shouldn't even be a question.
I have an iMac(Early 2009) running Leopard (10.5.8). Now I want to upgrade my OS to El Capitan (10.11).
The situation is this one:
✔ my iMac version is listed under the upgradable devices
✘ MacOSX 10.6.8 is required to be installed (due to Mac App Store introduction) on the iMac
Said that, after some search, I found this macworld article showing alternative methods to upgrade from 10.5.8 MacOSX version to a more recent one. This reading brought me to another solution:
The linked article hit my questions' topics but I did not deeply understand nor the configuration of the Apple ID on the fresh installed El Capitan nor the legal aspects of the solution.