In the 'header.php'

I changed the text that is displayed on the logo ....

now I get this message at the top of the page

Warning: Cannot modify header information - headers already sent by (output started at /home/printedt/public_html/includes/languages/english/classic/header.php:33) in /home/printedt/public_html/includes/init_includes/init_templates.php on line 78

What have I done wrong and how can I fix it?