GenericCommand worked :
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final ProcessInstance processInstance = ksession.startProcess("com.sample.bpmn.v1", null);
................
GenericCommand<Void> genericCommand = new GenericCommand<Void>() {
public Void execute(Context context) {
StatefulKnowledgeSession ksession = ((KnowledgeCommandContext) context).getStatefulKnowledgesession();
ProcessInstance processInstance = ksession.getProcessInstance(processInstance.getId());
WorkflowProcessInstanceUpgrader.upgradeProcessInstance(ksession, processInstance.getId(), "com.sample.bpmn.v2", mapping);
return null;
}
};