"Ошибка синтаксиса в инструкции UPDATE.", хотя вроде всё написано правильно.
private void button1_Click(object sender, EventArgs e)
        {
            string connectString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=BD1.mdb";
            con = new OleDbConnection(connectString);
            con.Open();
            string query = "";
            if (frm.radVal == 0)
            {
                query = string.Format("UPDATE Developers SET Developer_name = '" + textBox1.Text +"', Developer_specialty = '"+ textBox3.Text +"', team_id = "+ textBox2.Text +", Password = '"+ textBox4.Text +"' WHERE Developer_id = "+ id +";");
            }
            else if (frm.radVal == 1)
            {
                query = "UPDATE Managers SET Manager_name = '" + textBox1.Text + "', Admin_id = '" + textBox3.Text + "', Password = '" + textBox2.Text + "' WHERE Manager_id = '" + id + "'";
            }
            else if (frm.radVal == 2)
            {
                query = "UPDATE Admins SET Admin_name = '" + textBox1.Text + "', Password = '" + textBox2.Text + "' WHERE Admin_id = '" + id + "'";
            }
            cmd = new OleDbCommand(query, con);
            MessageBox.Show(query);
            int number = cmd.ExecuteNonQuery();
            Console.WriteLine("Обновлено объектов: {0}", number);
            //MessageBox.Show(cmd.ExecuteScalar().ToString());
            if (button1.Focused)
            {
                MessageBox.Show("Данные успешно обновлены");
            }
        }