These are 3 ways to change fonts on WordPress.com blogs.
(1) Changing font families, colors and size in text in posts or pages either post by post or page by page by coding into the HTML editor. http://en.support.wordpress.com/editors/font-size-color/
(2) Changing font colors in text in posts or pages either post by post or page by page using the #4 icon (Select text color – change the text color) in Row 2 the Visual editor. http://en.support.wordpress.com/visual-editor/#row-2
(3) Changing all font families, colors and sizes throughout the whole blog by purchasing an annually renewable Custom Design upgrade and using Typekit Fonts with Staff support. http://en.support.wordpress.com/custom-design/
Note: Any font changes to font families, colors and size in the blog title, tagline, post titles, page titles, categories and tags cannot be done without CSS editing.
P.S. I am a visually challenged person who cannot fathom why you have made the font on your blog so large. I think you probably don't know that all of us can change the font size of any site we visit on the internet very easily by using keyboard shortcuts to increase or decrease font (text) size.