At the top of your stylesheet, find this...
body {
margin: 0;
font-family: verdana, arial, helvetica, sans-serif;
font-size: 65%;
color: #000000;
background-color: #e5edf5;
}
Change the red number to something larger, perhaps 75 or 80%. Then have a look at your site. If you like it, you're done. If not, then you start to track down individual elements, like all H1 and H2 and H3 elements and change their sizes in the stylesheet. Basically you go through the stylesheet looking for all occurances of font-size and adjusting as needed.
But try the first thing I suggested first. It's easier. :yes:
Rob