Sorry, should have mentioned that the folders might not already exist and you may have to create them yourself.
If you can browse your FTP and find the style.css that is in /forum/forums/HOME/styles/e3d8bd/ then you're on the right track. That e3d8bd folder is where you need to place the top.html (the banner) for your current style. If you can't see the e3d8bd folder then something is amiss.
If you still want me to do it for you I can do, no problem.