I was going to make a snarky comment about the problem being in your
code, which we can't see.  But I got to thinking about what you could
have done to cause it not to work and remembered just how complicated
updating Swing components can be.  So I think your problem is that you
need to call revalidate() on your JLabel after you change the image in
your ImageIcon.  But I'm just guessing without being able to see your
code :-).

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

public class test extends JFrame {
    public test() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final Image newImage = getToolkit().createImage("kittens.jpg");
        final ImageIcon i = new ImageIcon("saturn.jpg");
        final JLabel l = new JLabel(i);
        JScrollPane sp = new JScrollPane(l);
        add(sp,BorderLayout.CENTER);

        JButton b = new JButton("Change");
        b.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                i.setImage(newImage);
                l.revalidate();
            }
        });
        add(b,BorderLayout.NORTH);

        setSize(400,300);
        setVisible(true);
    }

    public static void main (String[] args) {
        Runnable r = new Runnable() {
            public void run() {
                new test();
            }
        };
        EventQueue.invokeLater(r);
    }
}