Dear ZuriNet,
if you are still reading this thread:
The news on the right hand side has been added using the "Artikel einfügen (rechts)" module. This module just shows another article within the current article.
The module has been specified to show the content from the "Contenido News" article in "Systemseiten" -> "Teaser rechts".
This article gets its content from "http://www.contenido.org/rss/de/news" (RSS feed).
You can't change these news, you just can specify some other RSS feed...
Regards
HerrB