Headers already sent problem

I had wordpress installed for me, the multi blog option was included.

I was testing different themes to use, when I had this error appear :
Warning: Cannot modify header information - headers already sent by (output started at /home/droveall/public_html/wp-content/themes/wordpress-blue/functions.php:1) in /home/droveall/public_html/wp-includes/pluggable.php on line 697

I get a similar error on every page, I cannot access the dashboard.

I have disabled the plugins via FTP , but that hasn’t worked, is there any way I can uninstall the themes in the same way.