iStore theme comes with variety of typography settings. Almost all areas of the WordPress site has font face/styles that you can adjust from these sections.Besides the standard fonts, it includes latest Google fonts library as well. Head to Theme Options, Typography section to control the font settings. Along with font face, you can also adjust font weight, font subset and font size as well.

Go through this documentation section and on your left, it has all the sub-sections for font settings.