For changing the top section with the iPhone slider, you will need to edit the image URLs in the page sections listed at –
2) First section to change is the Intro page section and you will need to change the comma separated image URLs listed in the slider shortcode as seen below –
[iphone_slider direction_nav=true control_nav=false pause_on_hover=false image_urls="https://www.livemeshthemes.com/appdev/wp-content/uploads/2013/07/iphone-slide1.jpg,https://www.livemeshthemes.com/appdev/wp-content/uploads/2013/07/iphone-slide2.jpg,https://www.livemeshthemes.com/appdev/wp-content/uploads/2013/07/iphone-slide3.jpg"]
Just upload the images to the Media Manager and change the URLs above to point to your own images, just making sure the image sizes match with the original ones so that they fit inside the iPhone.
2) The second section is Showcase section with a custom animation. This also requires that you change the featured-app.gif image URL in the code (pls switch to HTML tab of the editor to handle this better) –
There is more detailed discussion on this section here if you need it –