JDBC How to update records in SQLite

Question

I'm trying to update records in my sqlite database when the button is pressed. I've tried everything and I'm at wits end, please help Here's the button code c is a Connection variable, index is an integer variable that represents user's ID in the db

            @Override
            public void actionPerformed(ActionEvent e) {
                przelewKw = Double.parseDouble(kwotaF.getText());

                nazwaDoP = listaDoP.getItemAt(listaDoP.getSelectedIndex()).toString();

                try {
                    for (int i = 0; i < nazwiska.length; i++) {
                        if (nazwaDoP.contains(idKonta[i]) && nazwaDoP.contains(nazwiska[i])) {
                            if (stanK[index-1] >= przelewKw) {
                                double roznica = stanK[index-1] - przelewKw;
                                try {
                                    String url = "jdbc:sqlite:D:\\SQLiteDB\\Bank.db";
                                    c = DriverManager.getConnection(url);
                                    c.setAutoCommit(false);

                                    PreparedStatement pstmt = c.prepareStatement("update Konta set StanKonta='"+ roznica +"' where IDKonta=' " + index +"'");
                                    pstmt.executeUpdate();
                                    System.out.println(stanK[index-1]);
                                }
                                catch (Exception exc) {
                                    System.out.println(exc);
                                }
                                finally {
                                    try {
                                        if (c != null) {
                                            c.close();
                                        }
                                    }
                                    catch (Exception ex) {
                                        System.out.println(ex);
                                    }
                                }
                            }
                            else {
                                JOptionPane.showMessageDialog(framePrzelew, "Zbyt mało środków na koncie", "Uwaga", JOptionPane.WARNING_MESSAGE);
                            }
                        }
                    }
                }
                catch (Exception ex) {

                }
            }
        });```