$(window).scroll(function() {
 if ($(window).scrollTop() > 550) {
  $('div.to-top-btn').fadeIn('fast');
 } else {
  $('div.to-top-btn').fadeOut('slow');
 }
});
$('div.to-top-btn').click(function() {
 $('html, body').animate({
  scrollTop: 0
 }, 1000);
 return false;
});

/* CSS */

.to-top-btn {
  width: 50px;
  height: 50px;
  position: fixed;
  bottom: 30px;
  right: 40px;
  border-radius: 100px;
  background: rgba(0,0,0,0.5);
  display: none;
  cursor: pointer;
 }
 .to-top-btn .fa-arrow-up {
  margin: 16px 0 0 16px;
  color: white;
 }

/* end css */