My brother has medical POA does this give him the right to change her life insurance to someone elsa

An agent under a Durable [Financial] POA might have the power to change the beneficiary of a life insurance policy depending on what that POA states.  An agent under a Medical POA does not. An agent under a Durable [Financial] POA might have the power to appoint a successor agent depending on what the POA states.  An agent under a Medical POA does not.