Dear Subash Arya
If i am getting you right,then reducing the layout size can be done by just clicking on layout size on menu bar.You just click it and fill the dimensions in it, and get the desired layout window.
Secondly if you want to add your simulation system to any manuscript or paper and it is of long size then you can reduce it by clicking at View>zoom percentage and you can select the % which cover your whole system and then snip it.
Thirdly if you want to change size of the subsystem(box which include some component) the you just click it on and drag the either side of box and stretch to increase and decrease it.
Hope i have covered all the possibilities and it will help you
Regards