How to edit text on sign up pages

I wonder if you could just point me in the right direction on something. I am trying to edit the copy on the sign up pages for the listing directory (on this page http://prelaunch.lovenew.co.uk/listings/signin/?redirect_to=http%3A%2F%2Fprelaunch.lovenew.co.uk%2Flistings%2Fsignup%2F)

I found the file in the FTP /subdomains/prelaunch/httpdocs/wp-content/plugins/directory/ui-front/general, but when I save it back there, it doesn't change the text.

Am I doing something wrong?