For New Blog Interface :
Now click on Edit HTML Tab.
You will get a warning page avoid and click on Proceed Tab.
#navbar{display:none; height:0; visibility:hidden;}
see in below image for clarity, and click on save template.
For old blogger Interface :
Sign into blogger, now click on Design tab.
Now click on Edit HTML Tab.
#navbar{display:none; height:0; visibility:hidden;}
see in below image for clarity, and click on save template.
and click on save template.