There are several ways of achieving this which includes adding CSS into your HMLT. But Google has made it relatively pain free or those of us who are not computer whizzes. If you would like to have a go, all you need to do is:
Once you have logged inGo to Blog Overview --then to Layout----
Click on Edit Navbar - A pop up will appear and you will be shown 6 Navbar Design, see picture below.
From there you can choose a navbar which compliments your blog of simply
Click on the last option, the Off button then Save and your Navbar will disappear.
If you change you mind, simply go back and click on the navbar which suits your taste.
How painless was that.