How do I change the css?

I am not a tech expert but I have managed to install Zen 1.39 with the free template EstoreNow. I am trying to edit the css and I don't where to find it. Is it /includes/templates/EstoreNow/css/(I am not sure which to file to pick). I want to change the background color of the navigation menu bar as well as the buttons. I also wanted to change "Welcome to BlingTheme" or delete it. Can any one help?

Thanks.

You'll want to start with reading the Customizing section of the FAQ/Tutorials. (link at the top of this page)