Hi s b
The changes from 3.x to 5.x are a lot. Now the project support BPMN2 models that are standard, so if you create a graph based on JPDL(or xml files) you need to update the parsers to XML format. If you are willing to do that, please let us know to see the results.
About migration there are some efforts being done, but at this point I think that the best option is to re model your business processes. That will allow you to understand the new languange semantics.
Greetings.