The headline addition is the external storage support, which lets you connect up to two 256GB-plus USB 3.0 drives to the Xbox One. You can also choose which of the drives is your default for installs, including the internal 500GB number. Not a bad addition considering current-gen game installs seem to often hit the half-century mark for GBs.
Meanwhile, the instant sign-in option lets you select a single user to instantly log in when the Xbox One boots - a timely alternative to Kinect auto-recognition. As for the new name sharing settings, you choose which pals to show your real name to, as well as "friends of friends." The proverbial cast of Joey, as it were. However, followers who aren't your friends will still only be able to see your gamertag.
To manually download the firmware just head to your system settings, or you can wait for it to download and install when the system's powered down and checks for updates. Also starting this week, you can get on with grabbing the first Games with Gold freebies on Xbox One. Max: The Curse of Brotherhood and Halo: Spartan Assault are available on the service now, though unlike on Xbox 360 you lose access to them when Gold membership runs out.