Uploading images – error

Hi,

i have a problem with uploading images (like many people).

The error i get =
The uploaded file could not be moved to /var/www/vhosts/domain.com/httpdocs/wp-content/uploads

i’m a designer and i don’t know much about webdevelopment, but i have access to plesk (on linux server).

i would like to know which folders should have which permissions.
my wp-content folder is set to 777. wordpress makes an upload folder in wp-content, but i cannot edit the permissions of that folder. but it is also 777.

the images upload folder is set to wp-content/uploads in settings > miscellaneous.

what else can i try to fix this?

Thanks a lot.