Apple moved all of its software update services for OS X Lion and later to the Mac App Store. But even though the method of delivery has changed, you can still download either a simple update of OS X or the full (combo) update, if one is available. A combo update includes all of the updates that have been issued since the last major update of a system.

Before you head off to the Mac App Store to perform any kind of software update, be sure to back up the data on your Mac.

The Mac App Store

If you select the Software Update item in the Apple menu, the Mac App Store will launch and take you to the Updates tab. If you choose to launch the Mac App Store by clicking its icon in the Dock, you’ll have to select the Updates tab yourself. That’s the only difference between the two options for accessing software updates.

In the Updates section of the Mac App Store, Apple software updates will appear near the top of the page. Usually, the section will say “Updates are available for your computer,” followed by the names of the available updates, such as OS X Update 10.8.1. At the end of the list of update names, you’ll see a link called More. Click this link for brief descriptions of the updates. Some of the updates may have more than one link. Click all of the links to get the full scoop on each update.

Applying the Software Updates

You can select individual updates to install or install all the software updates at once. To select individual updates, expand the “Updates are available for your computer” section by clicking the More link. Each update will have its own Update button. Click the Update button for the update(s) you want to download and install on your Mac.

If you want to download and install all of the Apple software updates in one fell swoop, click the top Update button, in the “Updates are available for your computer” section.

Combo Software Update

For most of us, the basic OS X software update is all we’ll ever need. I have sometimes recommended downloading and installing the combo update, and I still sometimes make that recommendation, but only if you’re having problems with the OS that performing a full install will fix, such as apps that repeatedly crash, Finder crashes, or startups or shutdowns that either fail to complete or take much longer than they should. You can usually fix any of these problems using other methods, such as repairing a drive, fixing permission issues, or deleting or resetting various system caches. But if these problems occur on a regular basis, you may want to try reinstalling the OS using the combo software update.

Installing a combo update doesn’t delete your user data or applications, but it will replace most system files, which are usually the source of the problem. And because it replaces most system files, it’s important that you don’t use the combo update willy-nilly. You’re unlikely to remember all of the custom configurations you set up, and getting everything back in the same working order ranges from frustrating to downright impossible. Also, since you’re basically performing a full install of the OS, it’s going to take much more time than a basic update does.

Downloading Combo Software Updates

When Apple releases a system software update, it may also release a combo update, particularly when the revision is minor, such as OS X 10.8.0 to OS X 10.8.1.

Combo updates appear in the Purchases section of the Mac App Store, with the same name as the OS you purchased in the past. For example, if you purchased Mountain Lion, you’ll see OS X Mountain Lion in your Purchases list.

The list entry doesn’t include a version number, but if you click on an app’s name, you’ll be taken to a details page for that app. The page will include the app’s version number, as well as a What’s New section. If you wish to download the full version of the OS, click the Download button.

If you see a dimmed Installed button rather than a Download button, it means you’ve already downloaded this version of the OS to your Mac.

You can always force the Mac App Store to let you re-download the app.

Once the download is complete, the OS X Installer will launch.

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