Just a quick problem I had recently...
PROBLEM: I want to change my email address or username for login in my Blogger account. But I want to keep the content of my blog. How can I do it?
After logging in, simply go to SETTINGS > PERMISSION. You can find the button Add Authors and add your preferred email address. Refer to the image:
For your convenience, you can open another browser and access there your new email address account and accept the author invitation. Obviously, you'll do this so you won't be log out on your Blogger account.
After accepting the invitation, go back to your Blogger account. Still under the PERMISSION tab, you can now see your new email address added. Grant yourself the admin rights.
Optional: You may delete the old email address.