Hi there,
In order to remove the "Leave A Comment" box, you will first need to make a change in your Screen Options menu.
You'll need to enable the Discussion box in the Screen Option menu, which you can read about right here:
http://en.support.wordpress.com/screen-options/
Once that's enabled, you can visit any page you'd like and scroll below the Visual Editor box and see the discussion options for that page. You'll need to uncheck both the boxes in that area and then click the blue Update button. The "Leave a Comment" box will then be gone from your page!