how to update a password providing a security question and previous password is correct

public void button1_Click(object sender, EventArgs e)
        {
            {
                SqlConnection con = new SqlConnection();
                con.ConnectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=c:\documents and settings\aquib\my documents\visual studio 2010\Projects\labelnameinsecondformtry\labelnameinsecondformtry\Database1.mdf;Integrated Security=True;User Instance=True";
                string q = ("select SEC_QUESTION,PASSWORD from Table1 where USERNAME='" + textBox1.Text + "'");
                con.Open();
                SqlCommand cmd = new SqlCommand(q, con);
                SqlDataReader dr = cmd.ExecuteReader();
                if (dr.HasRows == true)
                {
                    Form2 f2 = new Form2();
                    while (dr.Read())
                    {
                        f2.label1.Text = dr["SEC_QUESTION"].ToString();
                        f2.textBox2.Text = dr["PASSWORD"].ToString();
                    }
                    dr.Close();
                    con.Close();
                    f2.Show();
                }