Instructions
Deleting Files from a Full Memory Card
Turn on your GameCube with either the disc cover open, with no disc loaded in the tray, or by holding the "A" button on the controller while the system loads.
Press "Down" on the Control Stick until you reach "Memory Card Screen." Press the "A" button to access the memory card menu.
Navigate to a game file by using the Control Stick. Afterwards, press the "A" button and select "Erase." Press the "A" button again.
Push the "A" button over the "Yes" option to confirm the deletion process. When it has finished removing the data, repeat steps three and four until all of the data has been erased from the memory card.
Reformatting a Corrupted Card
Turn on your GameCube with either the disc cover open, with no disc loaded in the tray, or by holding the "A" button on the controller while the system loads.
Push "Down" on the Control Stick until you reach the option titled "Memory Card Screen." Afterwards, press the "A" button.
Wait until the system asks you to confirm the formatting process for the corrupted memory card (this happens automatically if the system identifies your card as corrupted). Push on the Control Stick to highlight "Yes" and then press the "A" button.
Another window will appear to inform you that it will erase the data. Select "Yes."