Canon EOS 5D Mark II Firmware Update Procedures page 4

(4-1) Connect the camera and the computer.
Rotate the Mode Dial to select <P> mode (or any mode other than Fully-Automatic Modes).
Insert a CF card that has been formatted in the camera into the camera.
Connect the camera and the computer with the USB cable, and then set the camera's power switch to <ON>.
(4-2) Start the firmware update.
Start EOS Utility.
Click the [Camera settings / Remote shooting] button.
Click [ ].
Click the [Firmware Ver x.x.x].
The firmware update file will be copied to the CF card by following the on-screen instructions to select it.
Follow the procedure from Step (5) onward on the camera.
The firmware update screen will appear on the computer screen.
Click [OK].