To remove nav bar on the top of a blogger blog simply follow below steps:
For New Blog Interface :
Sign into blogger, now it will show list of your blogs now click
on this icon 
and click on template.
and click on template.
Now click on Edit HTML Tab.
You will get a warning page avoid and click on Proceed Tab.
Now it will show your blog HTML Code,
now find (CTRL+F) ]]>
and above it paste this code
#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.
Now it will show your blog HTML Code,
now find (CTRL+F) ]]>
and above it paste this code
#navbar{display:none; height:0; visibility:hidden;}
see in below image for clarity, and click on save template.
and click on save template.
