Currently Being ModeratedJun 26, 2013 7:43 AM (in response to clangfeldt)
The first step in updating is to order Snow Leopard from the Apple on-line store ($20 US), install SL and on-line software update that to 10.6.9. Then, determine if you can go to Mountain Lion by looking at the compatible machines listed in http://www.apple.com/osx/specs and if you are on the list, go to the App Store and choose to buy Mountain Lion ($20 US), download and install. If you do not meet the ML specs you can go to Lion if you have an Intel Core 2 Duo or above processer and 2 GB ram, though 4 GB is much better. That is purchased by calling 1-800-MY-APPLE and paying the $20 fee for the download code that will be sent in a few days in an email with instructions for doing the download.
You can go from Snow Leopard to either Lion or Mountain Lion directly.
Currently Being ModeratedJun 26, 2013 7:47 AM (in response to clangfeldt)
Some early iMacs cannot run any higher than Snow Leopard 10.6. Lion 10.7 required a Core 2 Duo processor, someting the first Intel iMacs lacked.
Doing "About this Mac..." from your Apple menu will show your processor type.