Actually this is default (at least that is whjat I thought and have seen from my experience). But if you need to increase or decrease you right click in the package and choose package properties. There you will find a setting for how many items to run in parallel with the ability to change from 4 then save your package. I have a few packages that run 5 and 7 all of which when I changed work fine for me.
"Don't roll your eyes at me. I will tape them in place." (Teacher on Boston Public)