Your external hard drive may be the reason why your wii u is freezing...

[kanageddaamen]

The problem is most likely your hard drive and not the update actually. I had the same issue. The problem is Wii U USB ports are USB 2.0. If you have a bus powered hard drive (no external power supply) then it is a USB 3.0 device.

USB 3.0 increased the current that could be provided by each port, which basically allows for bus-powered drives. If you use one on the Wii U, it will draw too much current, the drive will shut down, and the Wii U will lock up sometimes.

It's easily solvable while still using your same drive though. You need to get (or make, as I made a post about a few months back) what is called a y-cable. Nintenod spoke about this a while ago. This allows you to connect the device to 2 of the USB port, providing double the current draw potential. They are very cheap and easy to find online and I have not had an issue since I connected my drive with one.

Note this is different from a "Y-adapter" which will allow you to connect 2 devices to one port. You want 2 male USB ends combining into a single female. Here is an example of what you want:

http://www.cellphoneshop.net/usbycable.html?cagpspn=pla&gclid=CI37rfjB77QCFQ-f4AodGFAA8w