Help about changing the width of every post

Hi there,
I am new to wordpress and just choosed a template but by mistake i made some changes and now don’t know how to restore them. Actually the space available for the post in the theme is very less and i wanna increase the post width of every post.
Demo about how i want the theme– https://demos.gabfirethemes.com/transcript/2011/04/29/bama-player-hurt-in-storms/

Original site :- https://gadgetpub.com/?p=25

I can remove that ad code and share it buttons but can anyone tell me how to change the width of each post??
Thanks in Advance.