Background problem- It won't expand

I was trying to upload a new background onto my forum. When I upload it, it allows me to, but it doesn't show on my forum. I learned that you have to set your background color to white, so when I did that. It still doesn't work. There is a small strip of background (the background is small). I remember their was a page where you can set your background option, such as it having you to expand the background. Can anyone help me stretch it out please?

You can stretch it via MS Paint. Or, just request it in the Graphics Design section of the forum.