Format memory cards. To begin formatting, choose a memory card slot and select . Note that formatting permanently deletes all pictures and other data on the card. Before formatting, be sure to make backup copies as required.
Do not turn the camera off or remove memory cards until the message  clears from the display.
Press and hold the O (Q) and S (Q) buttons simultaneously for over two seconds until C starts to flash in the viewfinder and top control panel; you can then press the two buttons (O/Q and S/Q) again to format the memory card shown by the flashing indicator in the top control panel.
If two memory cards are inserted, the flashing indicator will show the card selected for formatting. To select a different card, rotate the main command dial while the C indicator is flashing.
Do not turn the camera off or remove the battery or memory card during formatting.