Question:Q:Hi i want to change my iTunes account from Australia Store to US Store and i want to reset My balance.

See: Change your Apple ID country or region

If you have less balance available on your account than a single item, either use your credit/debit card to pay for the rest or contact iTunes Support using the link provided at the end of the article.

Contact iTunes Support and get them to remove your balance:

iTunes Support via chat or telephone

iTunes Support via email

Then, follow the steps I posted above.