My Camunda process engine has been running, at this time, I'd like to design a new process.
Do I need to restart Camunda process engine when I have finished new process in BPMN Tools?
Well, that depends how you use your engine. If it is a shared engine, just deploy the new processes and you will see that the engine will hold the old and new versions. If it is an embedded version, you could try to deploy resources via the REST api, but probably it is easiest to just restart and let the engine scan for new models.