Dear Jeremy,
Thanks. I was too lazy to go into the FTP. Somehow I was able to upgrade it somewhere else:
If you recall, I was unable to upgrade at “Plugins” from the dashboard screen. But I upgraded it successfully at “Updates” (right below “Dashboard” and “Home”).
My jetpack is now 3.5. I hope this piece of information will be helpful for the jetpack team to find out why the jetpack cannot be upgraded at “Plugins”. Thanks!