[Number One]

Hi,
I have two stores and I am interested in two different templates which I have seen for sale. One is full width of the screen and one is set to a specific smaller centred size. How difficult would it be to change the width setting so that both are the same width? And assuming it's reasonably easy to set the width, which is the best way to go, both full width, or both size limited and centred?
Thank you for any help,
D.