What does my father need to do to change his will?

In Missouri, you should make sure that the will is executed properly. This means at least two witnesses see your father sign the will and they subscribe their names as witnesses to the will. Additionally, in order to make the will self-proving, which makes the will easier to get admitted to probate, the witnesses must sign an affidavit (sworn statement) before a notary public certifying that the will is genuine and that all will-making formalities were observed. So you first step is to assure that the proper execution procedures have taken place to make it a valid will. In Missouri, after execution, you can file the will in the probate court in the county where the person resides or is domiciled. This is rarely done. Most people keep their wills in a sage deposit box or somewhere safe at home. Please make sure people know where the will is kept.