If I don´t want all uploaded files to be in the webserver root, wich syntax should I use in the graph upload page?
I´ve tried "./foldername/foldername/myfile.ext" and "../foldername/foldername/myfile.ext".
I think this may depend on your hosting service's directory structure.
For the Directory box, I have to use "/domains/myweather.com/public_html". If something like that works for your host, then add your custom upload folder to the end of that.