How to change the look and feel in NetBeans GUI Designer Preview?

Write this in your main:

try { 
    UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel"); 
} catch (Exception ex) { 
    ex.printStackTrace(); 
}

The only thing I can find is:

Inspector > Right click on your JFrame > Preview Design

You can edit the look of the whole designer if you like...

In <netbeans_home>/etc/netbeans.conf, append the following to the netbeans_default_options setting:

--laf de.muntjak.tinylookandfeel.TinyLookAndFeel --cp:p path\to\tinylaf.jar"

(substituting TinyLAF for wahtever LAF you are using)

change LaF using preview design will not change the look. it only going to show you how the look is but if you want to change it you have to go to source then look for this code if you did not find it click on + symbol and change the word Windows to what ever you like note:you have to change it for all the jframes to work well

try {
    for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
        if ("Windows".equals(info.getName())) {
            javax.swing.UIManager.setLookAndFeel(info.getClassName());
            break;
        }
    }
} catch (ClassNotFoundException ex) {
    java.util.logging.Logger.getLogger(login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
    java.util.logging.Logger.getLogger(login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
    java.util.logging.Logger.getLogger(login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
    java.util.logging.Logger.getLogger(login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}