Once you have added an advertisement, you can customize it using the button.
Customize The Landingpage Advertisement
Customization can be done easily using the builtin HTML editor.
How to change the image
Double click on the image, and the image manager will popup.
How to change the Text
Double click on the Text and change it.
How to edit the Code Directly.
Code editor is available on the top right corner. You could edit HTML/CSS direclty on it as well.