Your attached image looks as though you are in the "Format" ribbon. Have you tried to center the graphic using the "Home" ribbon (just as you would if you were centering text)? (I have no idea if the German version of MSWord is the same as the US version...I am just assuming).

Hi,

as I do not see any anchor on your page, I'm quite sure you inserted (imported) the grahics as an InlineShape (Mit Text in Zeile).

So what you could do:
- Center the graphics like text (Start > Absatz), or
- Transform the graphics into a Shape (Bildtools > Zeilenunmbruch > Vor den Text) in order to move the graphics as you used to do.

NP