Complete The Firmware Update - Canon EOS 5D Mark II Firmware Update Procedures

When the firmware update operations are finished, turn the camera <OFF> and remove battery from the camera
for at least two seconds. This will cause the new firmware to take effect after the battery has been reloaded and the
camera is turned on.
Format the CF card before using it again.
(5) Update the firmware.
The message on the left will appear on the LCD monitor, and the
camera will check the version of the firmware update file.
The screen shown on the left will appear on the camera's LCD monitor.
If you press the <SET> button, a confirmation screen will appear, so
check the firmware update shown, rotate the Quick Control Dial to
select [OK], and press the <SET> button again to start the firmware
update.
The message on the left will appear during the update.

(6) Complete the firmware update.

When the update is completed, the message on the left will appear on
the LCD monitor.
Complete the firmware update by pressing the <SET> button.
The firmware update is now completed.