To update your applications automatically, please arrange the following settings:
1. On the Start screen press or click on Store to open the Windows Store.
2. Swipe in from the right edge of the screen, and then tap on the Settings icon. If you are using a mouse, point to the lower right corner of the screen, move the mouse cursor up, and then click on Settings.
3. Press or click on App updates.
4. Set the Automatically update my apps option as Yes.
To check for applications updates manually just use the Check for updates option any time.
Please, see here for more details: http://windows.microsoft.com/en-us/windows-8/automatic-app-updates-help
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