Document Upload Problem

I just got WordPress installed and configured for the most part. I cannot upload docs though. It throws some errors about “parent directory permissions” and not being able to write to it. The error is quoted below:

The uploaded file could not be moved to /var/www/vhosts/thesewerschool.com/httpdocs/wp-content/uploads.
Warning: Cannot modify header information – headers already sent by (output started at /var/www/vhosts/thesewerschool.com/httpdocs/wp-admin/admin-functions.php:1986) in /var/www/vhosts/thesewerschool.com/httpdocs/wp-includes/functions.php on line 1346

Any help or direction would be appreciated.