How do I change my guild background?

[dancers-avatar]

Hello all,

my nub self has a few questions to the " how do I mod my guild's webpage"
from what I have understood from reading through the faq, the manage webpage options and forums; the theme our guild uses allows us to change the background image, the image on the top left side and the banner image.
I made one attempt at this and it did not look too pro :-( the images overwrote the page links and I was trying to have it so that it meshes the way it does now just diff images. I used .jpg images not .png do i need to upload .png files instead of .jpg?
I love the transparency effect of the theme and want to keep that. Second question is am I correct that we can replace the image for the banner completely? I made up an banenr with our guild bame and all but my attempt at replacing it failed.
Our site can be found on guild cafe here http://www.gamerdna.com/GuildHome.php?re=1&short=shards
Thank you in advance for you time and trouble in helping me with this.

pz,
Dale