Warning: Cannot modify …

Hi

When I try to load my page I get this message “arning: Cannot modify header information – headers already sent by (output started at /home/content/l/u/i/luisiher69/html/index.php:5) in /home/content/l/u/i/luisiher69/html/wp-includes/pluggable.php on line 850”. I did do some modifications to my theme yesterday but I tested it and it worked.

http://spanish-aid.co.uk/

Could you advise please?
Thanks
Luis