By default, WordPress displays comments that are ascending. This means that the oldest comments are on top and new contents are buried on the bottom (or other pages if your comments are paginated). To display your comments descendingly, paste this snippet into your theme’s functions.php or custom plugin:

//* Display comments in descending manner
add_filter ('comments_array', 'descending_comments');
function descending_comments($comments) {
	return array_reverse($comments);
}