Yes is it is possible to change your template header banner. To do so, simply follow these steps:
Log in in to your Tradekey account.
Go to Members Area.
Click "Trade Tools" at the top bar
Under the "Company Website" tab on the left panel, click 'Banner'
Select from a list of available banners of your choice or simply upload your own banner (dimensions: 740px x 150px, in JPG format only)