how to update database value

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ASP.NET

This is my code

protected void Page_Load(object sender, EventArgs e)
    {
        userdetails();

    }
   
   
    public void userdetails()
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("select * from freeuserdetails where UserName='" + Session["username"] + "'", con);
        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.Read())
        {
            txtuname.Text = dr["UserName"].ToString();            
            txtmailid.Text = dr["MailId"].ToString();
            txtdob.Text = dr["DOB"].ToString();
            txtmobileno.Text = dr["MobileNo"].ToString();
            txtaddress.Text = dr["Address"].ToString();
            cmd.Dispose();
            
        }
        con.Close();
 
    }
    protected void btnupdate_Click(object sender, ImageClickEventArgs e)
    {
        
        
        con.Open();
        SqlCommand cmd = new SqlCommand("update freeuserdetails set MailId='" + txtmailid.Text + "',DOB='" + txtdob.Text + "',MobileNo='" + txtmobileno.Text + "',Address='" + txtaddress.Text + "' where UserName='" + txtuname.Text + "'", con);
        cmd.ExecuteNonQuery();
        con.Close();
    }

if i click the update button the old database values are updated ........
How to update the database values...