This is actually a WordPress function…. when you have a page or post open in the editor, at the bottom will be a checkbox for discussion. Check the box to disable the comment form. If this does not show, at the very top click on the upside down tab labeled Screen Options and place a check by Discussion to show it below.
By the way, for the Showcase one, you can adjust the padding (space) around the image or slider from a setting in the theme options on the Header tab. By default it has 10px 0 as the padding which means 10px for the top and 10px for the bottom but 0px for left and right.