Well this is one of the major problems to many bloggers all around the world you can do this very easily Transfer Yahoo user id to gmail id is not at all a big task hear is what you need to do.
If you want to transfer the account
Get into the blog, using administrator account From Settings - Permissions, add a new blog member, using a suitable email address used by the person being given access.
Login to Google, under the email account targeted in step 1. Open the email received, and accept membership, using any valid Google account. Or setup a new Google account, if necessary. Note that the email account used initially, and the Google account may, or may not, be the same.
Login to the blog, using an account that currently has administrative access. From Settings - Permissions, make the new member an administrator. Be careful, and only add administrators who can perform reliably.
If you're transferring ownership, not adding an administrator
- Login to the blog, using the account that was just given administrative access. From Settings - Permissions, remove the old account.
>> (Note 1): If you're doing this in preparation to switching your Blogger, GMail, or other email account, do not discontinue the current account until you have executed, and tested, step 2.
Remember, though, that you can only login to one Google account at a time, from a single computer. If you have other abilities setup on the current Google account, you'll be constantly logging off and onto each account, as you switch back and forth.
>> (Note 2): Remember that Google authenticates using one account, for multiple tasks (Blogger, Google Apps, Google Mail, and others), using cookies. Be sure to clear cache and cookies (both cache and cookies, and the two are not the same), at the end of the procedure above. If you use one computer for all steps, you'll be logging off one account and onto another; in that case, you will want to clear cache and cookies after each step. Take it slowly and carefully.