Remove a Pop Up Screen

Hi Everyone,

I have a picture on my website and every time someone clicks on it a sign up form appears (that was set up a long time ago by a colleague) and I need to remove it. How can I do this?

I thought maybe it was done in Optinmonster but when I go into it, there is a note saying it has expired and I need to renew. I do not want to do this unless I have to. Does anyone know of another way?

Thanks,
Katina