Installing or Changing a Blogger new Theme

STEP 1: Go to Blogger.com 
Log in to the website. If you are already logged in, look for this window:

STEP 2:  Click the More Options link marked with green circle (third option from pencil Icon) and in the menu select Templates

Now you should see your blog's template Window . Click on Edit HTML. 

Now you should see your blog's template Next Window. Click on Backup /Restore from top right corner below the your account name.

Now you should see your blog's template Next Window. In this window You can choose new template or can backup your old template. It will be very useful if you backup your old template before applying a new template. For backup Click onDownload full template or for applying new template click on browse buttonchoose File and locate the ZIP archive you downloaded from this website and unzip/unrar it. (If you didn’t downloaded it yet go to websites: btemplates.com  Orbloggerstyles.com and download the template you like most)

In the folder contained in the archive, there are three files: license.txt, readme.txt and theme name.xml . For instance, if you downloaded the Gears theme, the .xml file will be named gears.xml or something similar. 
Now you have 2 options. 
Either open the .xml file in a plain text editor (like Notepad on Windows) and copy paste the contents to the edit template field. 
Or, use the restore template function to upload your new template.

Click the browse button and find the .xml file on your hard drive. Hit the upload button. 
Don't forget to save your template.

Hurray! Your blog has changed with new theme enjoy!