How to dowload and edit content of a website

The site you have linked to is a store for WordPress themes, so you would need to pay for and then download the theme files that they give you. You would then need to go to your own WordPress install and install them there (instructions for installing a theme incase you haven’t done this: http://www.wpbeginner.com/beginners-guide/how-to-install-a-wordpress-theme/).

Once your theme is installed, you will have the ability to customise it within WordPress by going to Appearance > Customize on your dashboard left menu. This will give you the options for customisation that are available with your theme.

If you have some knowledge of html then you can also customise your theme by going to Appearance > Editor and then choosing each of the files in the right menu to edit them directly. I wouldn’t recommend this option if you are new to WordPress.