I was still married and my son has my ex husbands last name n he also apperas on birth certificate and I wish to remove him can I do so and if so how can I go about that

Depending on where you live the father of the child (presumed father) is your ex husband. There may or may not be a challenge to it. Mostly it depends on where you live and how long it has been since the birth.

ANY question on law needs to include your general locale as laws vary by area.

IN all US states, when a child is born to a married couple the husband is the legal father. Consult with a local Family Law attorney to determine the feasibility of challenging paternity.