Admincp >> forum manager
reorder the forum numbers
parents/catagorys are different to forums and subs so should be something like this:
1 <--parent/catagory
-1 <--forum
-2
-3
2 <--parent/catagory
-1 <--forum
-2
-3
3 <--parent/catagory
-1 <--forum
-2 <--forum with subs
--1 <-- sub forum
--2
then simply save display order