** if you are using a Google email account, this login account cannot be changed.
How do I change the login name or password on my Google Account?
You can make changes to your Google Account by logging in to http://www.google.com/accounts and selecting the option to change your password.
There is also a link in the Blogger interface to take you to the appropriate place. You can find this link on your dashboard after you have logged in, and it will be next to your profile links on the right hand side.