Changing Fonts (and related settings ) In Wordpress

I am using wordpress for my blog/site. I am using Freshnews theme from woothemes as the theme for the blog.

Here is the link:
http://demo.woothemes.com/freshnews/

The font is not that good and it is way too small and the spacing is bad (too congested).

How do I change the fonts, size, spacing (line and paragraph) throughout the blog.

I know I would have to change it somewhere in the stylesheet. But where exactly and how?

And what are the ways to get this done?

Should I install a font somewhere?

Should I use webfonts (like google webfonts)?
What is the advantage in using this?

or what are the other ways?