If you add this to your theme I think it should work. Can’t test for sure 🙂
#ppom-box-3 > div > div > div > div > span{font-size: 18px;}
Change 18px to any size you like.
I see you are using the Art Gallery Pro theme, but I don’t see any evidence you are using a “child theme”. If you make these changes to the theme’s stylesheet and the theme is subsequently updated, you will lose your changes. So my unasked for advice is to create a child theme and add the new css there.
Your theme may have an admin function where you can add custom styles. Check for that first 🙂
Here is your theme’s style.css file:
http://www.chadsartworld.com/wp-content/themes/artgallerypro/style.css
Let me know how you get on.