Updating App Store Apps and System Software Enabling Automatic Updates Updating Apps Installed Without the App Store Upgrading to a Newer OS X Version Installing Updates in Legacy OS X Versions Community Q&A Software updates keep your computer and programs secure, fix errors, and provide new features.
Many apps that you install will get regular updates that can improve functionality.
Then, in the drop-down box, select the operating system under which you were previously running it (for example, Windows XP (Service Pack 2).
If this doesn't work, another solution is to run the older OS, such as XP, in a virtual machine using VM software, such as Virtual PC or VMWare.
If the validation tool won't run on your computer (and thus prevents you from downloading updates), the first thing to do is run the WGA diagnostics.