can’t access admin.php

i have no idea what i did. but whenever i try to access my admin page this warning comes up:

Warning: Cannot modify header information – headers already sent by (output started at /home/mocha/public_html/wp-config.php:24) in /home/mocha/public_html/wp-includes/pluggable.php on line 275

i really want to update my version of wp but i don’t want to do it until this is fixed first.