An update is now available for the Wii U which will upgrade your firmware to version 2.1.3. Here is a brief description from Nintendo:
Version 2.1.3 U available via an Internet connection includes the following improvements:
Further improvements to overall system stability have been made.*
*The previously announced system update, which adds new features and further improvements to the user experience, will be released in April.
You can read the instructions for performing a system update on Nintendo's official website via the link below:
How to Peform a System Update - Nintendo.com