when i try to pay with gift card it says

1017: Sorry, your balance is too low to complete this transaction. You have $10 remaining on your GameStop card. You can trade your full $10 GameStop card for $7.4 to use towards this purchase.

how can i trade a $10 game stop gift card for the said $7.4? so I can add that with another $10 game stop gift card to purchase a starter pack of hero seals