Here you can edit the html of your blog, you can also change your blog's template from here.
How to change template in Blogger.com ?
Note: Before changing your Blog's Template, If you have added gadget to your blog then please keep a backup of these Gadgets ( By copying the html/java and saving in a .txt file )
At first download the template( In most cases templates are provided in .rar format or in other formats, extract them and take out the .xml file, This .xml file you will upload to your blog ).
Click on Browse and Upload