You should have an attorney review the situation and prepare a notice to your principal, any health care institution or provider that has relied on your position as agent to date and may actually have a copy of the poa, as well as the named successor holder. It should be in writing with proof of delivery to the applicable parties and provide an appropriate resignation date so that there is no gap. If the original power was notarized, so should the resignation. If the poa is being used out of state, it may require other formalities. If your principal is non-decisional, other issues may be involved. There may be other factors to consider.