Files not deleiting and changing permissions doesnt work

For some content which I created in Panel. I can no longer edit or delete these files. I have tried deleting and changing permissions in terminal but to no avail.

With rm -rf I get:

rm: illegal option -- /
usage: rm [-f | -i] [-dPRrvW] file ...
       unlink file

With chmod -R 755 i get:
Operation not permitted

When I try and delete in the panel I get:
mdir(/opt/lampp/htdocs/caspar-paulie/content/1_workshop/project-e): Permission denied

With rm -rf / you will irreversible erase all files from the complete filesystem - but you have luck, it seems you do not have the permission to do so.

Also with chmod, you can only change the permissions of files and folders that are writable for you and the message from the panel shows the same.

It has nothing to do especially with Kirby, I would advise making yourself familiar with the concept of ownership and permissions on a UNIX-like filesystem.