The file is $JBOSS_HOME/standalone/configuration/standalone.xml. Find <socket-binding-group> and <socket-binding> there.
EDIT
There’s multiple ways to do this. The recommended way is to use the management console.
If JBoss AS runs on your local computer, open the URL http://localhost:9990/console/App.html#socket-bindings and edit the socket-bindings there. I tested it on Wildfly 8.1.0 Final, don’t know if the URL is valid for other versions of JBoss AS.