Change Headline & activate slider not possible

Hi everyone, I just installed related post and changes the headline from "related Posts" to "das könnte dich auch interessieren". Now I want to change the headline again into "Ähnliche Beiträge", but i do not know where to do it.
In addition, I would like to have the slider layout, but cannot activate it. I can chose and save settings, but there is no effect to be seen.
Deinstall and reinstall the plugin did not work for either problem. The website is still under construction and not online yet. I would be grateful for a solutiuon. Thank you and best regards, Anya