Press [2nd];
Press [MEM]; // The same key as [+]
Choose 7: Reset...
Press [→] twice to the ALL tab;
Choose 1: All Memory...
Choose 2: Reset;
Your screen will show the message "Resetting All..." Wait for a few seconds;
Your screen will show the message "Mem cleared" when it is done;
Do not use your calculator until after your proctor check the message on your calculator;
Summary: [2nd] -> [MEM] -> [7] -> [→] -> [→] -> [1] -> [2]