Alternatively, you can go to the Windows 8 page at Microsoft and download the update here:
Buy Windows - Microsoft Windows
I upgraded 8.0 last night on my SP1 and everything went as smooth as butter, even with programs like CS6, Lightwave3D, Office, and Painter X3 installed. I lost nothing.
Just remember to remove any external accessories, as well as the Micro SD card if one is inserted, before installing the update and you should be fine (I even removed the keyboard). If you leave anything connected (or inserted) to the main tablet, your mileage may vary.