How to increase site width?

Hello, This is my site - https://4holidaymaniacs.com/ On the left and right side, there is too much space. Is there a way to keep the left sidebar width same, but increase the width of the main content? Also, on the rest of the pages - https://4holidaymaniacs.com/2-weeks-in-namibia-detailed-itinerary-trip-report/, I am forced to use no sidebar, full width as content area is too small. I want to keep the content area this size and still add left side bar as there is lot of white speace on either side. Is it possible? Thanks so much in advance.