What to do:

From the Wii U Menu, select "System Settings".
The current menu version will be displayed in the top right corner.
Using the Left Stick, scroll to the "System Update" icon and press the A Button.

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Tap "Update" to connect to the Internet and begin the update process.
The length of time it takes to perform a system update varies depending on the speed of the Internet connection used. Please be patient.

Depending on the amount of new features and applications included, the system update may take an extended amount of time when performed(for some users it could take an hour or more to download and install). Do not unplug the power from the Wii U during a system update.