Rename label of "table of contents"

[Horacio Emilio Pérez Sánchez]

Hi,

I want to change the label of the "table of contents" section (in spanish 
called "Indice general") to "Indice". After searching for information, I 
tried using:

\renewcommand\contentsname{Indice}

in the preamble of my lyx document, but it doesn't work.

Could somebody help me ?

Thanks.