which font size would you like to change? where on the page?
look in your theme style.css file
body {
font-size: 62.5%; /* Resets 1em to 10px */
font-family: Arial, Helvetica, sans-serif;
color: #000;
background: url(images/bg.gif) #88cfde;
}
controls the overall font size….you could bump that 62.5% up a bit.
or this block here
.entry {
width: 100%;
overflow: hidden;
margin: 0px 0 0 10px;
font-size: 1.2em;
font-family: Bookman Old Style,Arial, Helvetica, sans-serif;
line-height: 20px;
}
is just the actual post font size….
really you can scroll through your style.css and change any of the font sizes to suit your needs