Wrong permissions with proFTPD

a few minutes ago I finished the setup of the LAMP stack and proFTPD. Now I wanted to upload my project to the ftp, but I keep getting these errors:

Case: deleting my php test file:

DELE test.php
550 test.php: Permission denied

If I try to change the persmissions like this:

chmod g+s /var/www
chmod 775 /var/www
chown -R www-data:www-data /var/www

I get the error: chmod: changin permissions of '/var/www': operation not permitted

Same happens with chown root/var/www

Any ideas/expericens with this?