How to edit style.css for bluemarine theme

I've been trying to edit the style.css located /themes/bluemarine/style.css. I've made the changes that I want to the style.css file but when I upload and replace the file the site does not reflect the change. It's been I while but I've done this in the past but now I cannot figure it out. I'm just trying to make a simple change to the header color so that is matches the banner I created.

Here is the existing code:

#header {
background-color: #69c;

And this is what I'd like it to be

#header {
background-color: #0d163d;

Any ideas? What am I doing wrong?

The site is http://snowmanage.com

Thanks,

Willy