How to change power of attorney from a sibling to another?

Double check the current Power of Attorney document.
Most often a successor or substitute agent is named in the document.
So too, may be found the circumstances under which the successor may assume responsibilities.

1. How was the Power Of Attorney drawn up, ie; by an attorney,in a bank, on line? ... reason asked, an attorney is not free and you do not need an attorney to change (or even create) a POA. 2.The person issuing the first POA still needs to be of sound mind, competent (meaning has not been deemed incompetent by physicians) they then Write and Sign (a notary seal as witness is best) a cancellation of the first POA, name them, then by the same means state by name the new POA (which also should be notarized.) After document is written, you should notify the one holding the first POA of the transfer, and also notify all impertinent entities of the change, entities that would need such information to ever enable the new POA to communicate in whom-evers name. Entities such as; Dr.s offices, Medicaid, Medicare, etc etc.

The only person who can change a Power of Attorney is the person who first authorized it. Example, if your parent wanted sibling A to be his/her POA but now wants sibling B to be his/her POA.

Usually the parent, sibling B will go to an attorney to have the change made.

....I cannot agree with "most often" - a successor agent is named. You must be aware that not all individuals has a "second best" also you must keep in mind there are several "different POA templates out there and not all have successor mentioned. If you who are answering are attorneys, remember not all use attorneys to draw the docs up in the first place.

(Excuse typos, and misuse of words per sentence) seems this (new) phone is editing as it sees best.

Personally I would never try to do a Power of Attorney on my own. Not even download forms off the internet. All it takes is one misplaced word or one missing word to create a landmine of issues.

The elder has to provide photo ID and have the doc notarized to begin with so what is your question? For change out to another POA it is the elder who does this.