Vicious Circle

Hi, I added some banner ad code (Javascript tag using the revive-adserver.com program we use) into the Header & Footer section.  

As soon as I entered the script, the edit page jumped to a page that displays the banner.   Now I can't get back to the Header & Footer page because as soon as I get to the page, it goes to a page displaying the banner graphic.   
I'm not sure how to get back in there and disable it.   The banner shows up when I view the page (not in the right spot yet), so it works anyway.   
 
How can I get back into the edit-page?  I somehow need to disable it but don't know where...
photos.strugis.com   

I did edit the template file directly and removed the code  /sy-layouts-custom/
and I cleared the cache in CloudFlare... 
I've used Grep and can't find any more instances of the code...   
But the banner still shows up.  

I forgot about disabling javascript in my browser!   Duh!   I did and was then able to see and delete the code.