Problem uploadin files

Hi,
I installed wordpress in my web page.
I changed the folder properties to 777 to make parent directoris writable by the server.

I still can’t upload any kind of files from my computer to my domain.
The error message I get is the following:

the uploaded file can’t be moved to /var/www/vhosts/mk-r.es/httpdocs/wp-content/uploads.

How can I solve the problem?
Thanks
Chiara