Amendment to partnership deed

Dear Members, If the Partnership Deed initially did not provide for remuneration/salary to be paid to working partner but if the same has to be added to the Deed, what is the procedure? There is a provision in the Deed that it can be amended by mutual consent of both partners in writing. Should a new deed be drawn up? Should the amendment be made on a stamp paper or ordinary letter head signed by both partners would be enough? Please advice.