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Slide the lock on your memory card to the unlocked position. Some cards, such as Compact Flash cards, have a mechanical lock that prevents accidental erasing or writing to the card.
Insert the card into your Canon camera and turn on the camera.
Related Reading: How to Format an SDHC Card for a Computer
Press the "Menu" button on the camera.
Select the "Card Operations" or "Maintenance" option from the menu -- on some Canon cameras, this option might be represented by a tab containing a wrench. Select tabs or options by using the navigational wheel on the camera and pressing the "Select" button.
Select "Format" and check "Low-Level Formatting," if that is the option you desire.
Select "OK" or "Execute" and confirm that you wish you format the card. Formatting will then commence and you'll get a message when it is complete.