Exactly what are you trying to do?
If you don't want a tagline, copy includes/languages/english.php into includes/languages/YOUR_TEMPLATE (where YOUR_TEMPLATE is the name of your custom template). Open includes/languages/YOUR_TEMPLATE/english.php with a good text editor like Notepad++ or Crimson Editor (both free downloads).
Around Line 11 find
Code:
//define('SITE_TAGLINE', 'The Art of E-commerce');
change it to:
Code:
//define('SITE_TAGLINE', '');
(NOTE: the two single quotes remain)
Save the file and FTP it to the correct folder on your website.