<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def change_user_name(self, usrname, newusrname, callback=None):
        '''
        Change user name.
        '''
        params = {'usrName': usrname,
                  'newUsrName': newusrname,
                 }
        return self.execute_command('changeUserName', params, callback=callback)