How can I clear my Apple Account balance?

This is a user to user forum, you are not addressing Apple here.

As users, much like yourself, we cannot remove the balance from your account.

You can either buy something more expensive than your balance and pay the rest with a credit card or if you have less store credit than the cost of a single item and cannot add a credit card to your account, contact Apple Support so they can clear it.

Click the blue link above to have Apple support clear your balance.