A power of attorney is a document that authorizes someone to act on your behalf in particular contexts. This person, called the agent, has the terms of authority that are described in the power of attorney document. Most such documents can be revoked at any time and are automatically revoked if you become incapacitated. The exception is the durable power of attorney, which persists beyond your ability to willfully revoke the authorization, up until your death.
Draft an entirely new document. The best practice for amending a durable power of attorney is to redraft the entire document, reflecting the additions or deletions of authority. This document then should be formally executed and witnessed like any new power of attorney, according to the laws of your state.
Revoke the previous agreement. State laws might specify acceptable methods for revoking a power of attorney, but it usually is sufficient to destroy all copies of the document and inform all third parties as to the revocation.
Execute an amendment. Another way to change a durable power of attorney is to draft a separate document that explains the changes to the original document. This must be signed and witnessed as if it were a new durable power of attorney, and the agent must be informed of the changes. This method is seen as problematic because it's possible that ambiguities and inconsistencies between the original document and the amendment can make it difficult to discern your true intent.