If you just wanted to edit the text you have highlighted then it's the name of a category, you can edit that text in the WordPress Admin section. Look under Posts > Categories. But if you wanted to change the styling of that Italicized text then you edit the style.css inside TwentyTen theme folder and look for .page-title span { } , its in line number 544.
Yeah perfect, thanks, that worked just fine, I used the following code in the child theme What about where it reads "categories archives", where do I change the style for that
Glad it worked The styles that affect that "Category Archives:" would be in .page-title { } in line #538 and #content h1, #content h2, #content h3, #content h4, #content h5, #content h6 { } in line #494.
Would be easier if you would install Firebug for Firefox and use its functions to show CSS of elements.