How to change picture at Home "Popular Destinations"

Dear Support,

How I could change picture of country at Home page in “Popular Destinations” section.
Please see http://travelwp.physcode.com/home-4/ at “Popular Destinations” section, your page have a country picture but after I download your demo, its not show.

Also what the picture resolution for this section (example 1400×700 px).

Thank you