I am trying to change the menu headings from the downloaded template "Northrend-Arthas".
I thought I found the right area in CSS under MenuCat, but changing the background setting seems to make no difference. It continues to load a file called Menu-HeadOpen2.gif.
Could someone please tell me how to bypass / fix this?
It's also in a javascript file loaded from the layout file. You'll have to use the Advanced Layout Options, find the javascript file that it's loading (It's called something like "MenuToggle.js"), download your own copy of it, modify it, then upload it to your Admin File Uploader.
Finally, you'll need to modify the layout.html file to point to the new file.
That SHOULD take care of that for you. I know it's a little tricky, but that's how that particular template is, unfortunately.