I'm not assuming that anyone has coding skills. In fact WordPress.com is a platform for those who aren't into coding at all. If we don't like the fonts the theme designer defines for our themes that's what the CSS upgrade can be used to address.
We can change all font families, colors and sizes throughout the whole blog by purchasing an annually renewable Custom Design upgrade and using Typekit Fonts with Volunteer and/or Staff support. http://en.support.wordpress.com/custom-design/#custom-fonts
In the CSS forum get assistance to identify and change the font selectors throughout the blog so the fonts are the (style, color) size you want appear throughout the blog.
Use the Text editor and code the font change for the body content in every post and page that you create before publication.