You can decide exactly how much funds each card has at any given time.
This means that it is completely up to you when you want to free up some committed funds from one card to allow payments to go through another card.
Moving part of application balance
Simply select the application, scroll down to Budget details and click Edit.
In the Application balance, fill in the amount you want this application to have, and save the changes:
If you are reducing the application balance, the extra will be moved to the main pool of funds as Available balance.
Moving the entire application balance
If you want to zero the balance within an application because it is unnecessarily withholding a large amount when the payment is not due for another 3 months, you can go to the top right of the application right above the card, and click More actions > Flush money.
All the funds in the card will be moved back to the main account and will be available to spend on other cards.