How do I upgrade to Lion from OS 10.5.8

Go to the Apple menu in the upper left, and then "About this Mac." If it says Power PC then you cannot upgrade beyond what it already has. If it says Intel then we can provide upgrade instructions.

Ah, I see. In that case, the highest OS you can get on it is Snow Leopard 10.6.8.

http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard

I'm sorry, but your Macs aren't compatible with OS X Lion and Mountain Lion. They are 64-bit operating systems, and the Intel Core Duo processor that your computers have is 32-bit. However, you can upgrade to Snow Leopard

Mac OS X Snow Leopard with the latest update has got the App Store, so you can install apps from there. The problem is that some apps, like iMovie, requires OS X Lion, so you will have to buy iLife '11 in a DVD on Amazon

The disk you will receive has version 10.6.3, which does not have the Mac App Store. However, you can go to the Apple menu and then Software Update, and update to 10.6.8 (for free), and that will have the Mac App Store.

You are welcome