To change the video in the first screen, set the path to it in src attribute.
<video preload="auto" loop class="cover-el" poster="img/theme/background/5.jpg" muted> <source src="video/travel.mp4" type="video/mp4"> <source src="video/travel.webm" type="video/webm"> <source src="video/travel.ogv" type="video/ogg"> </video>
In poster attribute set path to image that will be visible on devices that doesn't support video tag.