How can i change this part of the background?

i.e like this?:



And i have got template editing.....

c'mon!!!

I dont get, what are you trying to achieve?

i'm trying to change that part of that background where the red arrow i pointing to.

Right now, it's just plain white but i want to put a background pic in there....

Oh, find an image (make sure it is seamless, ie it doesnt appear to be looping), then go onto the ACP > Display > Pics Management > Advanced, and from there you can add a background image to be used

EDIT
There may not be an option for it, so you'll have to use some CSS, and it may only work on certain versions (thats phpbb2 as far as im aware) - best thing would be to ask kilsek how he did it.