As from version 10.8.3 of MacOSX (Mountain Lion) users do not need to login as an administrator to get the latest system updates from the Mac App Store. Even if you are logged in as a standard user, it is possible to view the available updates for updates.
- Open the Mac App Store
- Select the Update tab.
- Reload the page with the following shortcut: CMD + R
- Enter your administrator credenetials (login and password)
- Download the updates
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