如何通过从数据网格视图中选择行来删除和更新文本文件的信息

文本文件如下所示：

id,name,username,password
1,x,js,111
2,y,mm,222

我可以从文件中读取并将其放在DatagridView上，这就是代码

    private void buttonTadd_Click(object sender, EventArgs e)
    {
        FileStream fs = new FileStream(@"C:'Users'HP'Documents'Visual Studio 2008'Projects'BankServer'TellerFile.txt", FileMode.Append);
        StreamWriter sw = new StreamWriter(fs);
        sw.WriteLine(textBoxTNumber.Text +","+ textBoxTName.Text +","+ textBoxTUserName.Text +","+ textBoxTPassword.Text);
        sw.Close();
        dataGridViewTellers.Rows.Clear();
        StreamReader sr = new StreamReader(@"C:'Users'HP'Documents'Visual Studio 2008'Projects'BankServer'TellerFile.txt");
        string line;
        while ((line = sr.ReadLine()) != null)
        {
            dataGridViewTellers.Rows.Add(line.Split(','));
        }
        sr.Close();
    }