How do I edit the html files: themes/simplicity/master_pages/general.html and dnd.html? 

I have tried dev mode and debug mode both set to true, and then dev mode to true and debug to false, and then debug to true and dev to false and even whilst I'm refreshing I still can't edit it. 

I remember something to do with having to clear out "static" but I can't remember how to do that. Can you please help?

Thanks in advance.