private void button3_Click(object sender, EventArgs e)
        {
            Connect();
        }
        public void Connect()
        {

            NpAdapter = new NpgsqlDataAdapter();
            NpAdapter.SelectCommand = new NpgsqlCommand(query, conn);
            ds.Reset();
            NpAdapter.Fill(ds);
            dt = ds.Tables[0];
            
            deleteCmd();

        }

        // Setups the delete command.
        public void deleteCmd()
        {
            string query = "DELETE FROM Newspapers WHERE Id_newspapers = = \'" + textBox3.Text + "\';";

            NpAdapter.DeleteCommand = new NpgsqlCommand(query, conn);

            NpParam = NpAdapter.DeleteCommand.Parameters.Add(textBox3.Text, NpgsqlTypes.NpgsqlDbType.Text);
            NpParam.SourceColumn = "Id_newspapers";
            NpParam.SourceVersion = DataRowVersion.Original;


        }

 private void button3_Click(object sender, EventArgs e)
        {
         string query = "DELETE FROM Newspapers WHERE Id_newspapers = = \'" + textBox3.Text + "\';";
         NpgsqlDataAdapter da = new NpgsqlDataAdapter(query, conn);    
         }

 NpgsqlCommand command = new NpgsqlCommand("Update \"Newspapers\" \"Price\"=\'"+textBox4.Text+"\' WHERE \"Id_newspapers\" = \'" + textBox5.Text + "\';", conn);
 command.ExecuteNonQuery();

ОШИБКА: 42601: ошибка синтаксиса (примерное положение: "=")