Photoria Theme | how to change font

If you mean this theme http://www.wpzoom.com/themes/photoria/ then you’d be best served asking at the wpzoom support forum.

http://www.wpzoom.com/support/

That’s a commercial theme (that happens to be free) and we don’t support those here.

That said, if you create a child theme (using that as the parent theme) and identify the CSS then you can adjust or change the font in your child theme. The Firebug extension is really useful for that or even the “Inspect element” tool built into Chrome.