Change font-family in theme
My answer is assuming you are referring to WP theme Twenty-Sixteen

Your question is not a CiviCRM issue, if you have other questions that are directly related to your CMS you should find a CMS specific forum to get more detailed help.

Here is a link with the instructions your are looking for.
https://www.geekypeak.com/how-to-change-fonts-for-twenty-sixteen-child-theme/
Again, you might need to find a CMS specific forum or try Google.