The if (have_comments()) { ... } checks whether there is any comment on your post, and starts a loop to display them.
The comment_form() function is responsible to render the comment form. So, if you want to swap their positions, you should swap these two.
But, you should make sure you move both comment_form() and its arguments ($comments_args) above the comment loop, since this variable should be defined first, or the default fields will be used.
The easy way to do this is to select the entire <div id="comments" class="comments-area clear-fix">...</div>, cut it and paste of below the comment_form(). Pay attention to PHP open and close tags <?php & ?>.