This week's book giveaway is in the OCAJP forum. We're giving away four copies of Programmer's Guide to Java SE 8 Oracle Certified Associate (OCA) and have Khalid A Mughal & Rolf W Rasmussen on-line! See this thread for details.
Are you using the bundled Tomcat? You can undeploy war-files within Netbeans when you switch from the projects-view to the Runtime-view, selecting there your server and right-clicking on the webapp you want to undeploy.