Where do I edit bills after they're put in proof stage in Sage Timeslips?

When I want to edit bills (after they've been put in proof stage) where do I edit them? Do I edit the bills in the individuals slips in the slip list or do I go to Billing Assistant and edit the bill there?  And what is the difference between printing a batch of bills from Billing Assistant versus printing a batch of bills from "Generate Bills"?  Thanks so much for any help you can provide.