Locked out of my site after installing a theme update

I am trying to log in to my wp-admin and below is the message I am receiving. Please help!

Warning: Invalid argument supplied for foreach() in /home/asa5602/public_html/wp-includes/post.php on line 3588

Warning: Cannot modify header information – headers already sent by (output started at /home/asa5602/public_html/wp-includes/post.php:3588) in /home/asa5602/public_html/wp-includes/pluggable.php on line 876