Tex. Est. Code § 113.157

Notwithstanding any other law, the form of an account may be altered by written order given by a party to the financial institution to change the form of the account or to stop or vary payment under the terms of the account. The order or request must be signed by a party, received by the financial institution during the party's lifetime, and not countermanded by another written order of the same party during the party's lifetime.