A person who makes a will (a testator) may update or revise the will at any time during their lifetime if the testator has the required mental capacity (is of sound mind) and the document is executed or signed with the required formalities (such as witnesses and signatures), as provided by the state’s laws.

There are generally two ways to update a will—execute a new will (usually the best option) with the required witnesses, signatures, and other formalities—or execute a codicil (a supplement to an earlier will), with the required witnesses, signatures, and other formalities, as provided by the state’s laws.

Laws regarding the use of codicils and the required formalities for wills and codicils vary from state to state and are usually located in a state’s statutes—often in the estates code or probate code.

A testator who updates their will by executing a new will should usually destroy the previous will to avoid questions regarding which will reflects the testator’s true intent and to avoid competing wills being offered for probate (recognition by the court).

In California, a testator has the right to update or revise their will at any time as long as they have the mental capacity to do so and adhere to the legal formalities required for executing a will. These formalities include having the will signed by the testator and witnessed by at least two individuals who are present at the same time and understand that the document is the testator's will. To update a will, a testator can either create a new will or add a codicil. A new will should follow the same formalities as the original will, and upon its execution, it is advisable to destroy all copies of any previous wills to prevent confusion or legal disputes after the testator's death. A codicil, which is an amendment to the existing will, must also be executed with the same formalities as a will. The specific requirements for wills and codicils in California can be found in the California Probate Code. It is often recommended to seek the advice of an attorney when creating or updating a will to ensure all legal requirements are met and the testator's intentions are clearly expressed.