Prateek,
Although it is theme dependent, many of the structural elements for your pages design are contained in the themes .php files. Go to DASHBOARD > APPEARANCE > EDITOR and you will see the files that make up the templates and in the case of some themes, sections of your displayed pages. You can go into these files using the WordPress editor or a text editor and make changes to the theme template itself, which may allow you to make the changes you desire (be sure to work from a copy until you are satisfied).
Using the Twenty-Ten theme as an example, you can find the < body > information in the header.php file.