Changing categories to sub categories

I want to know how to move already created categories (with sub categories and products) under a new main category

I need to move root-level product categories into a master Product category also, but cannot see a Modify button to do this. In the Business Edition, open up an existing category in the Categories section, there is not Parent or main category setting that I can see. Can you tell me where this is, or am I in the wrong area to do this?

Found it. Looks like when I was setting up the testing items, I changed the original Products category into an actual product specific category. Apparently that one cannot be reassigned. My other categories I had created later all allow changing the parent category.