You may not find a guide which lists down all the steps involved in migrating your application from 3.2.x to 4.2. There's Upgrade guide for moving from 3.2.x to 4.0. You can find it at http://docs.jboss.org/jbossas/upgrade4/html/.
Then there's the wiki at http://www.jboss.com/wiki/Wiki.jsp where you will find some more relevant information. Also, go through the
If at all there's something which is not covered in these pages, then you can always post a specific question in the forums here.