Currently Being ModeratedOct 10, 2012 4:07 AM (in response to Eira)
To upgrade you must first purchase Snow Leopard, Mac OS X 10.6, available from the Apple telephone order department, 1-800-MY-APPLE in the US for $20. Then upgrade that on-line to 10.6.8 for free. You can then go to Lion by also purchasing a download code from that same number for $20 and download Lion, 10.7.5, from the Mac App Store. If your computer is compatible with Mountain Lion, http://www.apple.com/osx/specs you can skip the Lion step and go directly to Mountain Lion by on-line download for $20.