add.Update(upd);

 public partial class Form1 : Form
    {

        private DataSet ds = new DataSet();
        private DataTable dt = new DataTable();
        static string connstring = "Server=localhost;Port=5432; User Id=postgres;Password=4353;Database=Pohta;";
        NpgsqlConnection conn = new NpgsqlConnection(connstring);
        public Form1()
        {  
        
            InitializeComponent();
          //Открыть соединение 
            conn.Open();
        }
//Функция изменения
        public void Update(DataTable upd, string table)
        {

            NpgsqlDataAdapter add = new NpgsqlDataAdapter("select * from " + table, conn);
            NpgsqlCommandBuilder com = new NpgsqlCommandBuilder(add);

            add.DeleteCommand = com.GetDeleteCommand();
            add.UpdateCommand = com.GetUpdateCommand();
            add.InsertCommand = com.GetInsertCommand();

            add.Update(upd);
     }
//Вывести содержимое таблицы Newspapres в DataGridView
        private void button1_Click(object sender, EventArgs e)
        {
            
            string sql = "SELECT * FROM \"Newspapers\"";
            NpgsqlDataAdapter da = new NpgsqlDataAdapter(sql, conn);
            ds.Reset();
            da.Fill(ds);
            dt = ds.Tables[0];
            dataGridView1.DataSource = dt;
           
        }
//Кнопка сохранить изменеия
        private void button2_Click(object sender, EventArgs e)
        {
          
            Update((DataTable)dataGridView1.DataSource, "\"Newspapers\"");
        }
//явное изменеие
 private void button3_Click(object sender, EventArgs e)
        {
             
          string sql18 = "Update \"Newspapers\" set \"Price\"=" + textBox1.Text + " where \"Name\"= \'" + textBox2.Text + "\') ;";
            NpgsqlDataAdapter da = new NpgsqlDataAdapter(sql18, conn);
        }
}