I am trying to upgrade a 2008 MacBook Air from OS X 10.5.8 (Leopard) to 10.10 (Yosemite). I understand from the Apple web site that the minimum required version of OS X is 10.6.x (Snow Leopard) for an in-place upgrade. However, I am assuming —correct me if I'm wrong— that the pre-existing version requirement isn't relevant if doing a clean install from a USB boot disk or other media? In any case I have had trouble doing this, hence this post:
I have found several guides on how to create a bootable USB stick for Yosemite, and my colleague has kindly created one for me using her newer MacBook. The guide used is located at http://www.guidingtech.com/34311/clean-install-yosemite-os-x/. I have attempted the install using the stick, by pressing the alt key after power on and selecting the USB stick but I am then faced with a No entry sign and the Air shuts itself down.
I would like to know what the most appropriate approach would be to get Yosemite working (legally). I don't have a Snow Leopard disc, and ideally I'd like to do a clean install anyway.