A power of attorney is a legal document where you give authority to an agent (also known as an attorney-in-fact) to make decisions should you become incapacitated. A power of attorney is an estate planning tool that is only useful when you trust your agent. If you wish to remove the agent of your power attorney, you must terminate the agreement itself.
Draft a revocation statement. Obtain a blank revocation form from your local county or district courthouse. The form is very basic, being little more than a statement that the existing power of attorney is revoked as of the execution date. Sign and date the form and have it notarized (sign it in front of the notary). Most banks have notaries on staff, or there should be a notary at the court clerk's office.
The fact that your agent is a family member is irrelevant under the law. The only restriction is that you must be mentally competent at the time of the revocation. Revoking the authority of a relative agent is identical to revoking that of a nonrelated agent.
File your revocation statement with any applicable state agency or court. If your power of attorney was specific (for instance, a tax power of attorney before the California Franchise Tax Board) you will need to file your revocation statement with that office.
Maintain copies of your revocation statement in an easily accessible location, along with providing a copy of the revocation to any third parties that could have acted upon the previous power of attorney, such as your hospital.