May I charge to be a power of attorney? If yes, How much?

White a letter ( recommend notory on it, perhaps even another witness, each state has its own requirement) in that letter you inform the old POA that as of a certain date their duties have ended.

You write up and sign a new POA for the person you wish to give it to.

You can buy blacks at office supply stores, find them online or have them done by an attorney.

I personally can write my own and/or have blanks so they cost me nothing but the notary fee.