First steps and plug-in installation

Hi,
I bought and update Inverto today.
I already updated also the demo contents because I read the guide in the documentation folder “First steps”.

I already installed two plug-in : Contact form 7 and IshYoBoy Inverto Assets.
Now I have some doubts because for example I would like to change the first image background in the home page but I don’t understand how.
Also I found Demo – Revolution Slider and Demo – Widgets but maybe I need to install before some other plug-in… It is true?
I read in the documentation that I need to install Installing Revolution Slider or Layer Slider but my folder it’s empty….
So, can you help me to find the correctly steps to replace the image and set a video content us background?

Thank you