You may use your own image as your header in AffiloTheme. To do this, please follow the instructions below:
Log on to your WordPress dashboard. If you are an Affilojetpack member, you can login to your Wordpress site by going to the Affilojetpack members area and clicking on the name of your domain on the right sidebar
Click Header Styles on the AffiloTheme menu.
On the Header Image section, click the Upload button to upload the header image from your computer.