You will need to using something like firebug(or other developer tools) to find the specific fonts you want to change then edit the proper lines in css

http://www.tutorial9.net/tutorials/web-tutorials/quick-easy-css-development-with-firebug/

-Chris K

First of all; Thanx for you clear replies.
I'm getting to know the background of the theme better and better.

Is there any way to change the font site of the homepage?

Thanx in advance.