i created a c# windows login form and i am saving username or password to a text file but every time i use same username or password that i have saved before it takes new place in that text file.

But What i want is to replace the same username or password that is already saved in that text file.

this is my code:

    private void button1_Click(object sender, EventArgs e)
    {
        try
        {
            FileStream fs = new FileStream("data.txt", FileMode.Append,
            FileAccess.Write);
            StreamWriter sw = new StreamWriter(fs);
            sw.Write("Email ID: ");
            sw.WriteLine(textBox1.Text);
            sw.Write("Password: ");
            sw.Write(textBox2.Text);
            sw.WriteLine();
            sw.WriteLine();
            sw.Flush();
            sw.Close();
            fs.Close();
        }
        catch (Exception)
        {
            MessageBox.Show("Error", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            this.Close();
        }
            MessageBox.Show("DONE", "Done", MessageBoxButtons.OK, MessageBoxIcon.Information);
            textBox1.Clear();
            textBox2.Clear();
    }