Wow, the update servers are horrendous. 2.3.1 through the desktop client, 5 hours and then times out at the end and restarts. I've never had a 69 meg file take that long. And I know that it's not my connection.
Abandoned that and tried downloading using the link here. About halfway I get a timeout and it restarts again. Trying again. We shall see how it goes this time.
Honestly, Kobo needs to make the updates resumable.