Comment form remove website url link

I really like this theme and I appreciate that you have placed it up here for all of us to enjoy.

I am trying to edit the comment form to not show the website url textbox and I have tried many things but they are not working.

One thing I did try was to change it with css and doing so made the entire comment form vanish from IE but it was all 100% the way I wanted it on Firefox.

I have tried using the functions and comment php files in the templates folder and still no success.

Please direct me to where I place this and also what do I exactly put there.

I really do not want to have to redo anything (edit core files) because when I update WP they will all go away and I will have to do this all over again.