i have a site using the twentythirteen theme, i want

i have a site using the twentythirteen theme, i want to replace the header logo, i dont want to create a child theme and cannot even find where the images that are there now are located. I am new to wp and a previous designer created this site and i need to change the header and all the posts do not help me for this theme.

i am not sure how i can replace the images with one large banner in the header section. I just need help with this area only.

can you help me figure this out?
http://www.midwestsmokeout.com