rename name index and subject index

[Wolfgang Engelmann]

I would like to rename my 'name index' and 'subject index' to the German 
'Namensverzeichnis' and 'Stichwortverzeichnis' with

\renewcommand{\indexname}{Sachverzeichnis}


in the preamble, but this does not give the desired output in the pdf 
file. What would be the appropriate way of doing it?

Wolfgang