FTP user and group ubuntu - password not working

[webass]

Hello, I want to achieve, that FTP users I give access to only presentation media, not are able to delete files.

How can I do this?

Thx.
Andre

P.S.: I tried to set over the shell console (ubuntu) an ftp admin and a user and the user to a group, and then moved the files to the place where I wanted them to be, gave chown to the user group and all looked fine.
But the user cannot enter with the given password.
Tried also to re-change it on shell, but doesnt work over filezilall to loign as user

[webass]

I observed, that when I copy files as root user in shell over to a folder in a web users directory, they get 0:0 as user:group.
But still when the webuser logs into FTP with the credentials created as FTP user in panel, the user CAN delete what belongs to root.

How can I avoid this?

[mehargags]

chown -R root:root: <dirpath> should let the user's see (Read) the files but not Change/Delete