I found this at http://www.illinoislegalaid.org/index.cfm?fuseaction=home.dsp_content&contentID=5518#a=questions
You can revoke a power of attorney in 3 ways:
By destroying the document
By writing a letter that says you want to end the power of attorney relationship
By an oral statement or other expression
Destroying the Document
You can revoke a power of attorney by destroying, burning, or tearing the power of attorney document in a way that shows your intent to cancel the relationship.
Writing
You, or someone under your direction, can cancel the durable power of attorney by writing a Notice of Revocation.
See the “Notice of Revocation of Durable Power of Attorney” in the “Forms/Letters” section of this guide for an online program that will help you fill out the forms.
The Notice must be signed by a Notary Public.
By an Oral Statement or Other Expression
You can revoke a durable power of attorney by saying you would like the relationship to end. You must do this in front of a witness who is at least 18 years old. Then the witness must sign and date a writing saying that your statement to stop the relationship was made.
It was last updated July 2010. Can anyone verify that “By Oral Statment” information is still correct?