A principal may revoke a POA at any time by employing one of three methods. First, the principal may physically destroy all executed originals. Second, he or she can sign and acknowledge a written revocation (per R. S. 46:14-2.1). Finally, the principal may revoke by notice to the attorney in fact.
It should be noted that simply appointing another in a later POA does not in itself revoke an earlier POA, unless the subsequent POA expressly provides. N.J.S.A. 46:2B-8.10.
Prudence dictates that the principal maintain a list of the person or people to whom an original has been given.