From your dashboard, click on 'expense cards'.
Click on 'my expense cards'.
Click 'view card groups'.
From here you can view all of your card groups, along with the card group balance and currency cards.
Click on the 'switch balance' tab.
On the left, select the currency you would like to switch from and the amount.
On the right, select the currency you would like to switch to.
Click the confirmation button and then click 'switch balance' to complete the transaction.