Do I have to alter my divorce decree in order to take my fiance's last name?

My ex-husband and I divorced 4 years ago. I decided to keep my married name because we have a son together. I have recently gotten engaged and want to take my fiance's name when we get married later this year. I have been told that since it doesn't state in my divorce decree that I wish to go back to my maiden name, I would need to have my papers altered before I can change my name even though I am not returning to my maiden name. Is this correct?