From Nikon:
Modifications enabled with this firmware upgrade
Only the camera(s) indicated above can be used to upgrade UT-1 firmware. Firmware updates can also be perfomed for you at Nikon service centers.
Confirming the firmware version (using the D7100)
Download the Nikon UT-1 Communication Unit 1.1 firmware update: Windows | Macintosh
Firmware installation instructions (English, PDF): Windows | Macintosh
B&H carries the Nikon UT-1 Communication Unit.