Here are the links to various posts related to deleting comments:
How to delete comments
Delete comments utility
How to delete own comments in other people's blog
And if you moderate comments via email, accidentally deleted someone's comment and want to repost it, refer to What to do when you accidentally deleted a comment and want to republish the comment
This FAQ is under construction. As a temporary measure, refer to Blogger FAQ which contains a listing of post under various topic, or use this online spreadsheet - Blogger related posts spreadsheet. Use ctrl+F to search for topics.