The Blogger has added new feature of updating robots.txt file.This file instructs to search engine what is allow or disallow to search engine, By default path of file is main directory.Type your blog URL / robots.txt and you will see the contents of robots.txt file, if this is not exists in main directory then all search engine consider that robots.txt file is not exists on server.
Steps to Change Robots txt in Blogger -:
1. Type your Blog URL / robots.txt in Internet browser. ( eg. www.example.com/robots.txt )
2. For backup of robots.txt, copy the existing contents and save in notepad file for your future reference.
3. Login in Blogger Account.
4. Go in Settings > Search Preferences
5. See Label Custom robots.txt , choose yes to update robots.txt file.