Here is how to do it.
1.First of all, go to list of blogs in your WordPress Dashboard
2.Click on Blog Admin link below the name of blog that you want to delete.This takes you to mentioned blog’s dashboard.
3.Find the Tools section
4.Click on Delete Blog
5.Follow The instructions (choose the one you desire from dropdown list)
6.Confirm the email which you get at your registered mail address.
7.Your blog is Deleted.