If you wish to cancel your Blogger account, you are unfortunately out of luck. There is no way to cancel a Blogger account.
You can, however, delete all information associated with the account. Delete all of your blogs and edit your profile to remove any personal information. Any comments that you left on other blogs will remain visible.
Deleting the e-mail address associated with your Blogger account will render you unable to access the account, so you should not do this until you have deleted all of your blogs and removed personal information from your profile.