If you ordered your website from BT after 24th April 2014, you have access to a new control panel where you can manage and update your website. Please click here to learn more about how to update your website.
If you ordered your website on or before 24th April, log in to your Control Panel, (i.e. go to www.yourdomain.com/siteadmin - but replace yourdomain.com with your website address), and click on Page editor.
From here, you'll be able to update the title and description of the page.