If you already submitted the form for filing and it has been accepted by the IRS, you can't change it. You will have to file an amended return later to make the change. If you do not have a dependent and meet the other requirements, you can't file as head of household. You would have to file married filing separately unless the person you are still married to agrees to file married filing jointly.
Head of Household filing status qualifications:
1. You are not married or “considered unmarried” on the last day of the year. You are considered unmarried if you lived apart from your spouse the entire last 6 months of the year.
2. If "considered unmarried" you file a separate return from your spouse.
3. You paid more than half the cost of keeping up your home for the year.
4. You have a qualifying child (whether or not you claim the dependency exemption) or you claim a dependency exemption for a “qualifying person” who is related to you and who lived with you in the home for more than half the year. An exception is a parent does not have to live with you to be a qualifying person.
