Error in modify theme

Hi friends.
Accidentally extinct information into the html of the header now I am receives the the next error messages. How I can resolve?

Warning: Cannot modify header information – headers already sent by (output started at /home/aldeia/public_html/blog/wp-content/themes/default/functions.php:1) in /home/aldeia/public_html/blog/wp-login.php on line 12

Warning: Cannot modify header information – headers already sent by (output started at /home/aldeia/public_html/blog/wp-content/themes/default/functions.php:1) in /home/aldeia/public_html/blog/wp-login.php on line 24

ERROR: WordPress requires Cookies but your browser does not support them or they are blocked