Nikon D6 Reference Manual page 1009

Reset All Settings
Reset all settings except [Language] and [Time zone and date]
to their default values. Copyright information and other user-
generated entries are also reset. Once reset, settings cannot be
restored.
We recommend that you save settings using the [Save/load
menu settings] item in the setup menu before performing a
reset.
Firmware Version
View the current camera firmware version.
G button U B setup menu
G button U B setup menu
B The Setup Menu: Camera Setup 957