A person who is mentally competent enough to understand the meaning of what he is doing can change his POA at any time for any reason. His POA cannot change it -- for example pass it on to another relative -- only the principal can make changes.
Valzena50, could you re-write your question, I am unable to follow what you are asking. Please tell us who is "he", and if it is "he" who wants to change the Power of Attorney or if it is someone else who wants to change it. More information would be helpful :)
If it is the person who assigned someone as his POA wants to revoke it he can. And assign someone else. He is the only one who can.