documentclass[serif]{beamer}
begin{document}

begin{frame}
    Step 1: Show some text
    begin{itemize}
    Step 2 item  show this item (text)
    Step 3 Show the image  % Image want to be in a central position
    Step 4 Hide the image
    step 5 item Show a new item (text)
    end{itemize}
end{frame}
end{document}

documentclass[serif]{beamer}
begin{document}

begin{frame}
  onslide<1->{Theory on Brontosaurs}
  begin{itemize}
  item<2->  Brontosaurs are huge

    only<3>{%
      includegraphics{beeduck}%
    }%
    onslide<4->{%
      vphantom{includegraphics{beeduck}}%
    }%
  item<4> Brontosaurs do not look like bee ducks
  end{itemize}
end{frame}
end{document}