To change Header Layout in Squarespace, you need to do these.
#1. First, access your edit mode
Suppose your site is: elf.squarespace.com
You can add /config after to access edit mode, so the URL will be:
http://elf.squarespace.com/config
#2. Next, click EDIT on the top left of the site.
#3. Hover on the Header , and click EDIT SITE HEADER
#4. Next, click EDIT DESIGN on the right side
#5. Next, click on Layout
Then choose the layout you want
