Workitem confusion

Hi,

for my PO workflow , a workitem is getting triggered when a PO is created and it goes to the approver inbox , before the approver approves it , the Workflow initator goes and do some changes in the PO, so again workflow is triggered and a new workitem comes to approver inbox.

now in approval inbox he is having two workitem for the same PO so now he wants that only the latest be dere else all should be deleted.

Please help me