To change a principal's password use the kadmin change_password
command, which requires the "modify" administrative privilege (unless
the principal is changing his/her own password).  The syntax is:
     change_password [options] principal
     
The change_password option has the alias cpw. 
change_password takes the following options:
     
For example:
     kadmin: cpw david
     Enter password for principal david@ATHENA.MIT.EDU:  <= Type the new password.
     Re-enter password for principal david@ATHENA.MIT.EDU:  <= Type it again.
     Password for david@ATHENA.MIT.EDU changed.
     kadmin:
     
Note that change_password will not let you change the password to
one that is in the principal's password history.