Delete script on my website

Hi all!

On my website (http://livestreamsports.nl/) you can find the following script:

<script type=”text/javascript” src=”http://nl.ads.justpremium.com/adserve/js.php?zone=15855″></script&gt;

I tried to delete this script, because we don’t want to work with Just Premium anymore. I’m using Filezilla to add scripts to my files, but i can’t find in which file this script is implemented in.. How can i discover which file i need to change? I’m already looking for 4 hours now…

Thanks!

Floris