How to change font size in the posts?!

Hi, I completed my blog but I can't understand how to change the size of the font used when you write posts. Indeed it is really too little and reading is not comfortable for my visitors Can anybody show me the procedure?? Thanks!

[karl94]

Ti ho risposto nel forum in italiano: http://forum.it.altervista.org/wordp...-del-blog.html.
Scrivi però in uno dei due forum, non in entrambi!