Can't upgrade WordPress

Hi

I’ve been asked to update a WP site that someone else has created. One (of a number of) problem is that I am unable to update WP to the latest version. When I try via the dashboard I get the following:

Downloading update from http://wordpress.org/wordpress-3.7.1-new-bundled.zip…

Unpacking the update…

Could not create directory.: /httpdocs/site/wp-content/upgrade/wordpress-3.tmp

Installation Failed

I then thought I’d do it manually but when I go in via FTP I can’t find any WordPress install.

Any help would be most welcome.

Phil