New stage size...follow up

I did a search and came up with a partial solution for this issue, but don’t quite know how to implement it.

I’d liek to resize my stage in my .fla without having the registration point in the upper left hand corner (kind of like resizing the canvas from the center point in photoshop).

I’ve seen it suggested to use _root.x and _root.y or something like that, but don’t know how to implement this. Any way to easily expand the stage from the center point? (or even right point?)