Below are the directions from the Nikon website. It is for the D800E, but the process will be the same for the D4.
(Not the most user friendly thing)
Firmware Upgrade Instructions
If you are comfortable with the process of upgrading your camera, use the basic instructions. If you require more support, use the detailed step by step instructions which contain helpful images linked below.
Basic Firmware Upgrade Instructions
Power the camera from the AC adapter unit or use a fully charged battery.
Create a new folder with an appropriate name on your computer's hard drive.
Download the Windows (.EXE) or Macintosh (.DMG) file from the links at the bottom of this page to the folder created in step 1.
Run the downloaded file to create a folder called D800EUpdate which contains the firmware D800E_0102.bin file.
Use a card reader or similar device to copy the D800E_0102.bin file to the root directory of a formatted memory card.
Insert the memory card into the camera's primary memory card slot and turn on the camera.
Select Firmware version from the camera's setup menu and follow instructions displayed to upgrade the firmware.
After the upgrade is complete, turn the camera off and remove the memory card.
Access the Firmware version item in the camera's setup menu to confirm that the firmware has been upgraded.
Windows:
Detailed Firmware Upgrade instructions Macintosh:
Detailed Firmware Upgrade instructions