A. Edit Site Header
#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:
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 to edit
B. Edit Header Font
#1. Click the Site Styles icon
#2. Click FONTS
#3. Click Assign Styles
#4. Click on each option to change the Header Font