The plugin is hosted in NetBeans plugins repository at. http://plugins.netbeans.org. Open the Plugins menu from the Tools top menu.
From the opened window, navigate to the Available Plugins tab, select the checkbox for the JRebel plugin and click Install button.
Hit Next button to proceed with the installation until you reach the dialog screen suggesting the a restart.
The plugins comes with the latest stable version of JRebel bundled with the plugin so you are all set after the IDE restarts.