Trying to change "Important Links" Sidebox Header

Hi all, I'm doing my best to wade through all this programming stuff, and have almost got my site where I want it looks-wise. My last problem is replacing the "Important Links" sidebox header with an image I have created. I have managed to change the other sidebox headers, but not this one as it goes with the EZ-pages. I have looked all over the FAQs for my answer to no avail. I have no idea where to change it! Can anyone help please?
http://www.goodbloom.net/shop

Thanks!
Holly

Copy includes/languages/english/extra_definitions/ez_pages_definitions.php into includes/languages/english/extra_definitions/YOUR_TEMPLATE/ez_pages_definitions.php and make the changes in the YOUR_TEMPLATE folder (of course, YOUR_TEMPLATE stands for the name of your custom template).