Question about editing Woothemes: Mystile with Child-Theme

I am having a delimma that could very classify me as a newbie to wordpress, which I am so I ask for mercy in your answers as these questions may come across as kind of stupid.

I am trying to edit the Mystile theme from Woothemes and I want to make a lot of changes. Before I ask my questions, I would advise referring to my site for reference to my questions. www.nicolasmoy.com

Moving forward,

In the header, it says "Nicolas Moy". I would like to erase that and input a custom logo. However, what I can't find out is how to edit it without tampering with the parent theme.

Everywhere I read it says to make a child theme, which I did. But now when I use Firebug to read the css and find the right file. I notice it is in a file called Brown.CSS.

So I upload a copy of Brown.CSS to my child theme folder and make the changes in there and nothing happens...

What am I doing wrong?

Can I only make the changes in the Style.css file that was originally made when I made my child theme? If so, how does that change the components in other css and php files?

I appreciate your patience and look forward to hearing any words of wisdom on this...

Nick