I just purchased QuickBooks 2013 and it says I need Version 10.7.3 or higher. I currently have 10.6.8 and when I try to do a software update is says I am up-to-date. Do I need to purchase an upgrade?
Choose About this Mac from the Apple menu, verify that your Mac has at least a Core 2 Duo(not Core Duo) CPU and at least 2GB of RAM, phone the online Apple Store, and order a download code for Lion.
If you want, open the Mac App Store and try purchasing Mac OS X 10.8. It won't allow the purchase on a configuration which can't use it.