Changing Banner

[*k.a.t.e*]

This is my first time with a myBB forum so I'm really lost I want to use this image:

http://img99.imageshack.us/img99/8987/izabel1xw0.jpg as a banner

and have it centred but but I have no idea where to start and all the codes confuse me!! I'm using the ChrystalWhite theme....could someone tell me simply how to do it?

[The Chosen]

http://support.createmybb.com/showthread...45#pid2445

That should help.