Editing Error pages in Jahia 5

Hi All,
 
Another Jahia 5 question.
 
I have tried editing jsp/jahia/errors/error_404.jsp directly but my
changes were not reflected.  Restarted, touched files, etc. without
success.  

Am I missing out a step, is this the correct place to edit the messages?
I could not find any documentation on this and any advice or support
that you can offer would be greatly appreciated.
 
Kind Regards
 
Graham