JBPM 4.4 vs JBPM 6.2

I am planning to use advance version of JBPM i.e. JBPM 6.2. Currently my project is using JBPM 4.4 but there are issues with JBPM4 DB tables which are accessed internally by JBPM API. I need inputs regarding this udgradation activity:

1. Since existing workflows will be continue to use. So is there any impact on existing workflows implemented by JBPM 4.4?
2. Both the versions will use same JBPM tables or will be different tables?
3. What is advantages of JBPM 6.2 over JBPM 4.4?
4. What are up-gradation steps to be carried out without impacting existing one?