The most important things you'll need to switch Wii Us are a SD card capable of holding all the data, and both systems to hand, fully updated and each with a GamePad attached. If you don't have your original Wii U, you'll need to contact Nintendo support. Also, be aware the transfer formats the new system before transferring data across, and also formats the original after the process. So when it's over you'll have your new Wii U with all your old Wii U data on it and nothing else, while the old Wii U will be a blank slate. For more info, check out Nintendo's detailed instructions.
Finally, if you - like us - get frustrated with having to relocate the GamePad when visiting the eShop, those woes are over now. Yes, the update also introduces eShop browsing using other peripherals including the Wii Remote, Wii U Pro Controller and Classic Controller.