Change Status

Hi,

Right now 5th step working with
Automaticaly changes the order status to “Processing (paid)” and notifies both the costumer and the store owner;

But we want to change status own way like
When status “Processing” or “Prtially Paid” at time we want as “Completed”.
Not want “processing” or other.

Is there way to change using any filter or with callback function?

Let me know if any solution or if not then how can we change.