You can follow these steps to change your current login id of blogspot to a new email or login id.
Steps as follows:
1. Login to Blogger using your current gmail email address.
2. Click on Settings on Dahboard for the blog you wish to transfer in case you have more than one blog set on blogger. Now, click on Permission under Settings tab.
3. Click on “ADD AUTHOR” under Blog Authors. Now type your second gmail address and click on Invite.
4. Now check your second gmail account and open the message from blogger. Click on the link provided in the email and sign in with your second Google Account to confirm the invitation and start posting to this blog as guest blogger.
5. Follow the step 2 and you will now see your second account as Guest under the Permissions sub tab of Settings. Now click on the “grant admin privileges” and confirm your action to grant the admin rights to your second email.
6. That’s it. Now you can delete your first email address or leave it with Guest privileges.
Note: You will have to do the same for every blog you have with blogger.