The deed is originally under my ex husband's and my old married name. However, during the divorce the house was refinanced and now the mortgage is only under my name (my new married name). How do I change the deed to my new married name and take my ex husband's name out.

I assume the disposition of the house was covered in the divorce?

Contact the register of deeds (or whatever your town/city/county calls it) and ask about the procedure. Its possibly as simple as producing proof of transfer (the divorce) and proof of name change.