Hello Guillermo,

To move your picture to top, you should change
style=”background-position: 50% -50px;”

to
style=”background-position: 50% -50px;margin-top:20px;”

Of course, you can use any image you want. If you want to change that picture, add the CSS rule below to your Appearance > Customize > Custom CSS section:

.blog .hero {
background-image: url(http://www.fantasticus.nl/sandbox/wp-content/uploads/2017/08/Fantasticus-Marco-Borggreve-copy-3.jpg) !important;
}

Don’t forget to change the URL of image to desired one.

Thanks,
Piotrek