Sometimes it appears to be stuck, but you just have to wait and it eventually completes. It might be a bug with updating the text and the progress bar, rather than the download being actually stuck.
You could also try the same trick as when you are getting the infamous error about the data being corrupted: Launch "internet options" (you can search for that in Windows's search bar) and click on "delete..." and in the next popup "delete". (This merely cleans the download cache directory, so it will force the updater to redownload.) I don't know if it will help in this situation, but you can try.