Can't acces WordPress dashboard

So recently I’ve been having some problems with WordPress. Most have been resolved but this one.
I can’t seem to access my WordPress dashboard. It comes up with this error

Warning: Cannot modify header information – headers already sent by (output started at /home/mysite/public_html/wordpress/wp-content/themes/red-riding-hood/functions.php:39) in /home/mysite/public_html/wordpress/wp-includes/pluggable.php on line 934

I’ve looked over the coding and everything seemed fine, but I am extremely inexperienced when it comes to WordPress.

My website is monsterious. My wordpress is located on the homepage as well.