i want to CHANGE current username and password

public int DLChangePassword(string UserName, string Oldpwd)
{
    con.Open();
    SqlCommand cmd;

    String sql = "SELECT * FROM tbluser WHERE UserName=@UserName AND Password = @Password";
    cmd = new SqlCommand(sql, con);
    cmd.Parameters.AddWithValue("@UserName", UserName);
    cmd.Parameters.AddWithValue("@Password", Oldpwd);
    SqlDataReader reader = cmd.ExecuteReader();
    if (reader != null && reader.HasRows)
    {
        con.Close();
        return 1;
    }
    else
    {
        con.Close();
        return 0;

    }
}
public string Update(string UserName, string Newpwd)
{
    con.Open();
    string str = "Update tbluser set Password=@Password where AdminName=@AdminName";
    SqlCommand cmd = new SqlCommand(str, con);
    cmd.Parameters.AddWithValue("@AdminName", UserName);
    cmd.Parameters.AddWithValue("@Password", Newpwd);
    cmd.ExecuteNonQuery();
    con.Close();
    return "success full change";
}

public int BLChangePassword(string UserName, string Oldpwd)
{

    return obj.DLChangePassword(UserName, Oldpwd);

}
public string BLupdate(string UserName, string Newpwd)
{

    return obj.Update(UserName, Newpwd);
}

protected void btnChangePwd_Click(object sender, EventArgs e)
{
    clsBLayer obj = new clsBLayer();
    if (txtCurentPwd.Text != txtCurentPwd.Text)
    {
        lblMsg.Text = "Retype Password Miss-match Try Agan";
        txtCurentPwd.Text = txtNewPwd.Text= "";

    }
    else
    {
        int a = (int)obj.BLChangePassword(txtCurentUserName.Text, txtNewPwd.Text);
        if (a != 0)
        {
            lblMsg.Text = obj.BLupdate(txtCurentUserName.Text, txtNewPwd.Text);
            txtCurentPwd.Text = txtReptPwd.Text = txtNewPwd.Text = "";
        }
        else
        {
            lblMsg.Text = "User And Password not Exist";
        }
    }
}