There should be an update wizard thing in the setting menu somewhere.
With the Wifi you don't really have a choice of version number, I think. It might update you to the latest version directly, if you're not already running it. Do you still have little page numbers on the right side of a book? Those were removed in later firmware, and a progress bar added at the bottom. It's hard to tell what to prefer... personally I hate the progress bar and modded it away as much as possible (unfortunately not entirely).