For most osCommerce and CRE Loaded sites, you can set the master meta tags in the file /includes/languages/english/header_tags.php.  This is a good options for those looking to make the site more SEO friendly.

You may access this file through an FTP client, but I would suggest you first save a backup copy of the original file before you make any changes and upload an edited version in case you need to revert back to the original settings.

Also, with the CRE Loaded stores, you have the option of manually editing the Meta Tags (title, description and keywords) on both the category pages and individual product pages via the Admin area of your site in the "Categories/Products" module.