
Changing folder location. How?
By default, the superuser's home folder is located inside system/data/
folder. It is important that you change the user's settings (from the FileRun control panel) and set the home folder path pointing to a folder which is located outside the public area of your web server (ie. outside www
).
I searched for an hour but could not find any instruction to do this. I also could not find this feature under Superuser's control panel.
Answer

Control Panel -> Users -> Edit User -> Permissions -> Home Folder.
It's right there...

I did this and after that I could not upload any files anymore. The error ist:
"File copy failed: CopyFile error: /var/www/temp/phpl0VvYJ could not be copied to /var/filedir/myfile.txt"
how to fix this?

Sounds like the permissions of the folder "/var/filedir/" do not allow PHP to make changes. The recommended action would be to check the folder's permissions and change accordingly.

Many of the control panel fields have a question mark button (?) on the right side. Use it for getting more information. For example, on this particular field you will notice it says "absolute path". Do not use "/../" paths with FileRun, it will only cause you problems.
If you do not know the absolute path of a folder on your server, the best people to ask for help is your hosting service tech support.
Customer support service by UserEcho
Control Panel -> Users -> Edit User -> Permissions -> Home Folder.
It's right there...