how to update userid and password using c# windowsform

ok riddhi
i tired changing only the password but still getting an error
this is the code:
and this is the error:

 private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                OleDbCommand command = new OleDbCommand();

                string query = "select UserName from UserTable  where Password='"+ textBox2.Text +"'";

                command.CommandText = query;

                OleDbDataReader reader = command.ExecuteReader();

                while (reader.Read())
                {
                   // string a= Convert.ToString(textBox1.Text);
                    //string b = Convert.ToString(textBox2.Text);

                   
                    string Password = reader["Password_U"].ToString();

                   

                    if (textBox2.Text == Password)
                    {
                        connect.Open();
                        command.CommandText = "update UserTable set Password_U = @pass where UserName =@username";

                        command.Parameters.AddWithValue("pass", textBox5.Text);
                        command.Parameters.AddWithValue("username", textBox1.Text);


                        command.ExecuteNonQuery();
                        connect.Close();
                       
                    }
               
                   
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show("Invalid UserId or Password,Please Fill the Fields Correctly" + ex);
                connect.Close();

            }
        }
    }
}

Hi..

Your logic is wrong dear.... Usernames must be unique.. Passwords can match...

Username must not be changed... It is a wrong practice.