If you want to do that in the editor you can select the objects, right click on that, and select wrap selection (shortcut key is return I think).
If you want to do it when running the game you can do this:
Global number scale=0.5
Global number centerx=320
Global number centery=240
Start of layout
— sprite: set x to (self.x-centerx)*scale +centerx
— sprite: set y to (self.y-centery)*scale +centery
— sprite: set width to self.width*scale
— sprite: set height to self.height*scale
That will scale around any center instead of just the object centers.
To have actual resize handles at runtime is a bit more involved. There is a resize handle example you should be able to find with the search I think.