Lastly i posted Tutorial 1 for installing blogger templates but it is valid only for new Blogger codes.Here is the one valid for old also.
After login, click on "Template".
Click on "Edit HTML"
Scroll down and on the left side, click on "Revert to Classic Template" and click "OK"
Open your new downloaded template from your desktopp using any text editor, i.e. Notepad and click "Copy"
Go back to your Internet browser and Ctrl+V (Paste) and click "Save Template Changes"
Congratulations ! You have installed your new template.