The shops title is contained in the includes/languages/english.php file. Open that file and search for this string
To change the title, you edit the word osCommerce. Be sure to leave everything else in place.
A better method of changing titles is to install the Header Tags Controller contribution. This will allow you to have unique titles and meta tags for all pages in your shop, which is very important for getting better search engine rankings.
Posted in: OsCommerce