MainStack subStack, I am lost

[René Micout]

Hello,
I have a main stack (MS) with 2 sub-stacks (SS1) (SS2).
I want change this hierarchy > new main stack = SS1 with 1 sub-stack (MS) with his own sub-stack (SS2)
Before changing:
MS
	SS1
	SS2
After:
SS1
	MS
		SS2
I turn in all directions, when I refer SS1 as main stack other stacks disapears, when I want to designate MS as SS : impossible.
I am lost
Thank you for help
Bon souvenir de Paris
René