How to remove a JPanel then add another one in, properly?

Ok, heres all of the necessary code.

Java Code:

package cyentw.utility.cutilities;

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.net.URL;
import java.util.Scanner;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Launch extends JFrame implements ActionListener{

        private JFrame frame;
        private JButton button;
        private JPanel panel;
        private JPanel panel2;
        private JPanel panel3 = new Panel3();
        private JPanel panel4 =  new Panel4();

        public static void main(String[] args) {
                new Launch();
        }
        public Launch()
        {
                
                frame = new JFrame();
                panel = new JPanel();
                panel2 = new JPanel();
                button = new JButton("button.");

                frame.setSize(500,500);
                frame.setLocationRelativeTo(null);
                frame.setTitle("CUtilities");
                frame.setName("CUtilities");
                frame.setDefaultCloseOperation(EXIT_ON_CLOSE);

                panel.setSize(500,500);
                panel.setLayout(null);
                frame.add(panel);

                panel2.setSize(350,500);
                panel2.setLayout(null);
                panel2.setLocation(160,0);
                panel2.setBackground(Color.white);
                panel.add(panel2);

                button.setSize(150,50);
                button.setLocation(5, 15);
                button.addActionListener(this);
                panel.add(button);
                
                panel2.add(panel4);

                frame.setVisible(true);
        }
        @Override
        public void actionPerformed(ActionEvent e) {
                if(e.getSource()==give)
                {
                                        panel2.remove(panel4);
                                        panel2.add(panel3);
                                        panel2.revalidate();
                        panel2.repaint();
                        pack();
                }
        }
}

//CLASSES PANEL3 AND PANEL4 BOTH EXTEND JPANEL, HAVE A LAYOUTMANAGER OF NULL, HAVE LOCATION 0,0 AND SIZE 350,500, HAVE 2 COMPONENTS EACH, AND ARE SET TO VISIBLE.

Hope this helps :)