which version of jBPM and JBoss Tools are you using? I'm using jBPM3 and the beta of Jboss Tools 4.. I bring up the process definition XML in the Eclipse process editor and click the menu for deploy process.. If you are using the previous version I believe there is a deploy process button on the deployment tab in the process editor.. Should be described in the tooling docs somewhere (don't have that in front of me so I can't quite it)
Good luck
Gary