You will need to go directly into Dashboard>Appearance>Editor and secelt the style.css. In there you will find a line that says font family: and then shows what the default font is. You will need to change this to the font you want to use then save. Make sure you keep the semicolon (;) at the end of the line or you may break the CSS and have to manually fix or replace the file for the site to work. hope that helps!