As you may have noticed Lion (10.7) is no longer available in the App Store. Apple intentionally pulled it from the App Store so people would go right to Mountain Lion (10.8) instead. As of today the latest version of Mac OS X is Mountain Lion, so you might as well just install that, but you don’t want to or if you machine doesn’t support it then you’ll want to go with Lion.
Lion (10.7) isn’t available to purchase thru the App Store, but you can still get it for $20 from Apple directly by calling 1-800-MY-APPLE (1-800-692-7753). Don’t bother with 3rd party sources (eBay, Amazon, Craigslist, etc). It’s only $20 from Apple and you are 100% sure it is the right version and not a scam.
Apple will send you an email to download Lion, instead of sending you DVDs like they do with Snow Leopard. Order it, get the email, download it and you are good to go.
You can find out what OS X version you are on by clicking on the Apple icon, then select the “About This Mac” menu item. The number under the Apple logo is the version you are on. 10.5.x is Leopard and 10.6.x is Snow Leopard.
If your machine can go all the way up to Mountain Lion (10.8) then don’t bother going to Lion. If you do you’ll spend an extra $20 because each upgrade is $20. Go from Leopard to Snow Leopard ($20) then Snow Leopard to Mountain Lion ($20).
If you can’t go to Mountain Lion, then you still need to get Snow Leopard installed because you can’t go from Leopard to Lion or Mountain Lion directly, you must first get Snow Leopard (10.6). Read my post “How to upgrade from Leopard (10.5) to Snow Leopard (10.6)” for more details on how to do that.
Like I mentioned above, before you order Lion make sure you don’t want or can’t to go to Mountain Lion. Going from Snow Leopard to Lion is $20 and going from Lion to Mountain Lion is $20. Once you are on Snow Leopard you can go directly to Mountain Lion and save yourself $20.
If you really want Lion then give Apple a call and order it for $20. Like I mentioned above instead of a DVD they will send you an email with a link to download Lion.