Logo is too small

I received my logo in jpg format and saved it in my media file yet when I try to upload it the logo is way too small. I have tried to make the image larger but after some research realized I need to code the header to be wider (I think…)

I am not sure what code to enter to where to enter it. I have never written any code before either.

http://www.theedgeofchic.com/wp-admin/#welcome/steps/title