Thesis 1_7 Custom Header

I’m sure this topic has been covered before but I’m going slightly crazy trying to learn how to customize by blog.
I was told that Thesis was very easy to customize so I bought it.
A friend helped me put up a new header but is too busy to teach me how to customize things myself, which is what I really want to do.
I’ve been going round and round, reading posts and watching video how-tos but I still don’t understand why I can’t do this and I’m getting very frustrated.
Can anyone point me in the right direction?
My blog.

This is how it was left last night but the colours are wrong, (I don’t know why) and it isn’t centred.

Can I do something with this to make it sit right?
*/

.custom #header #logo a
{
display:block;
background:url(https://www.armyofknitters.com/blog//wp-content/themes/thesis_17/custom/images/AOK_HeaderLOGO_900x130.gif) no-repeat;
width:900px;
height:130px;
color:#C7E1EC;
text-indent: -9999px;
padding-top: 0em;
padding-right: 0em;
padding-bottom: 0em;
padding-left: 0em;
border: none;
border-top: 0em;
border-right: 0em;
border-bottom: 0em;
border-left: 0em;
margin-top: 0em;
margin-right: 0em;
margin-bottom: 0em;
margin-left: 0em;
}

Do I need an FTP thingy with Thesis 1_7?

Any help is greatly appreciated!