Mo. Rev. Stat. § 473.143: Revocation of letters on finding will.

1. If, after letters of administration are granted, a will of the deceased is found, and probate thereof granted, the letters shall be revoked, and letters testamentary granted.

2. If a will is proved, and letters thereon granted, and the probate thereof is afterward set aside, the letters shall be revoked, and other letters granted of the goods unadministered.