WordPress Tutorial for Beginners
Modify Your WordPRESS Title and Tagline
The theme customization page allows you to modify your site's title and tagline and see how it will look on your actual site immediately. To do this, expand the Site Title and Tagline group of settings and alter the text. As you type you will see the new text showing up in the preview on your right side. Once you're happy with the result, simply click on the big Save and Publish button.
Hope this WordPress Tutorial clear most of your doubts about modifying Site Title and Tagline. You can also go through rest of the WordPress Tutorial posts. So that you can familiar yourself with WordPress without anybodies help