Just divorced and need help with a tax question.?

I have just gotten divorced, and have four children. The divorce decree says she will claim them as dependents as well as herself. She is unemployed. All year I have been claiming married and 6 exemptions for Federal and State of Missouri. It's the middle of the year now, and I make about 990 a month gross. If I start claiming zero and single and allot 15 federal and 10 state will I owe at the years end?