Formatting a memory card will erase all data stored on it so make sure you have a backup of all your important data before following this procedure.
To format your memory card go to Menu > Apps. (Applications) > Gallery highlight the Memory card and select Options > Memory card options > Format memory card. On Asha Touch devices when in the Gallery long tap on the Memory card and then select Memory card options > Format memory card.
The memory card inside your Nokia device should ONLY be formatted using your Nokia device. If you attempt to format your memory card in another device such as a PC, your memory card may not work properly.