Is it possible to upload data to the server?
in acp / system / files /

That area is showing items uploaded in content as attachments. You cannot manually upload to that area

Is it even possible to upload data?

16 minutes ago, peberl said:

Is it even possible to upload data?

What do you mean by data? If you meant attachments, then yes that is possible. 

rar  files or other formats

Edited January 14Jan 14 by peberl

You can upload those to posts, yes. As long as they are allowed in System>Settings>Posting

Thank you