It appears that main bone in my armature (moving which moves entire armature and around which every other bone rotates) is my left hand’s middle finger (look at screenshot)
How do I make my “main bone” (around which other bones are supposed to rotate) my torso (the one that lays on 3D cursor), aka how it’s supposed to be? Armature created by skin modifier’s “create armature” button
Object Mode > Shift S > Cursor to Origin > Grab your armature and mesh > F3 > Origin to Cursor
Didn’t work (no effect)
The “root” bone is whichever bone has no parent. As the finger bone in your screenshot does have a parent, the problem is not the “root” bone, the problem is that your origins are in the wrong place. You need the origins of the mesh and the armature to be the same, at the World Origin. You’ll also want to Ctrl + A > Apply All Transforms on both the mesh and the armature
Finger bone in my screenshot doesn’t have a parent, actually, making it the root bone
As far as I can see, my origins are in place correctly, so I actually need to reparent bones so that my torso bone becomes the root
That’s going to be a pain to pose, but that’s all right if it’s what you want.
Try this:
Note that this is an extremely old thread, so it may not work anymore.
meaning that i’ll have to change all parents manually, huh?
I hoped that there is an other, more automated way to do it
Sadly that’s the only way. Your rig is simple enough that it shouldn’t take long, though 
