Big Noob, how can i delete data from the server forever

I have no understanding for that program. I was working for a company which gave me a laptop with that program on. No i want to delete my data forever from the server, so nobody can download it again, because i will not working anymore for that company.

The problem is when i delete the data it is in the next day back there.
I trie right mouse click and delete: The result: Data is there in the next day
I trie the commnad "download and delete" but here the data was only downloaded but not deleted.

I have the login data and password also the passwort for the wlan from the company, if it needed so far...

Please help, iam a big noob

That's probably how the server is configured. We cannot help you with that. You need to contact your server/network administrator.