You can change your filing status from married filing jointly to married filing separately by filing an amended return using Form 1040-X. However, this must be done before the due date of the original return, without regard to extensions. Once the due date has passed, you cannot change from a joint return to separate returns for that year.
the only exception i can see to this is if you could not legally file a joint return under US tax laws.
so we need to know more about your situation since you say you have a spouse which means you are married
