Find your stylesheet folder for the template you are using. (If you have not installed a CUSTOM template, then your CSS folder will be in your CLASSIC directories.)
Find this part of the CSS code:-
PHP Code:
A.category-subs, A.category-products, A.category-subs:visited, A.category-products:visited {
color: #3093df;
font-size: 0.9em;
text-decoration: none;
}
You will make adjustments to the part that says font-size: 0.9em
Try using 1.0em or 1.1em or 1.2em (to go larger) and 0.8em or 0.7em or 0.6em to go smaller.
Please note: your COLOR (#3093df) will be different from mine.