joomla template modification

is it possible to get rid of the green image and replace the header with a banner for this template?

http://joomla15.siteground.com/?template=siteground-j15-68

Yes, of course.
Just ask if you want help on removing it and adding a banner

You just have to replace the image with your own image. The image is:

templates/siteground-j15-68/images/headerimg.jpg
390px wide
266px tall