For the product name as displayed in the Product List (after a search, e.g.):
content.css (line 237)
.productResultsWrapper .middle h2 a {
color:#2D6191;
font-size:20px; /*this is where the title size is set */
font-weight:bold;
text-decoration:none;
margin-bottom:0;
line-height:20px;
}
For the product name as displayed in the detail page (if you click on it from the Product List Page) is dictated by the value assigned to the h1 tag. You could either change the value of h1 tag (common.css - line 18) but you may need to see what else is sized according to that tag before changing it.
Alternatively you could create a class for 'WADAPageTitle', add it to your stylesheet and then apply it to your details page.