The room sample slider is found on the room_sample.html and it is based on slick slider.

The images from the slider are located in app > images folder and they can be changed from the following code:

<div class="hg-room-container">
 <div class="room-containter-image">
  <div class="hg-room-gallery">
   <div class="cont-img"><img src="images/room_12.jpg" alt="room-image"></div>
   <div class="cont-img"><img src="images/room_13.jpg" alt="room-image"></div>
   <div class="cont-img"><img src="images/room_14.jpg" alt="room-image"></div>
   <div class="cont-img"><img src="images/room_15.jpg" alt="room-image"></div>
   <div class="cont-img"><img src="images/room_16.jpg" alt="room-image"></div>
   <div class="cont-img"><img src="images/room_17.jpg" alt="room-image"></div>
   <div class="cont-img"><img src="images/room_18.jpg" alt="room-image"></div>
  </div>
 </div>
 <ul class="slider-nav container">
  <li><img src="images/room_12.jpg" alt="room-image"></li>
  <li><img src="images/room_13.jpg" alt="room-image"></li>
  <li><img src="images/room_14.jpg" alt="room-image"></li>
  <li><img src="images/room_15.jpg" alt="room-image"></li>
  <li><img src="images/room_16.jpg" alt="room-image"></li>
  <li><img src="images/room_17.jpg" alt="room-image"></li>
  <li><img src="images/room_18.jpg" alt="room-image"></li>
 </ul>
</div>

.hg-room-gallery triggers the slick slider and the .slider-nav triggers the thumbs underneath the big slides.

The styles for this gallery are found in app/style/scss/elements/_roomslider.scss