Do you have two separate email addresses that are connected two blog? Maybe you aren't sure how to merge them. Well, one way is to make one address the admin of the two blogs. Read more for more details
Number 1 step you should do is to choose which email address you want to make it dominant (that is, the one that controls the two blogs). For example, say that I have two account, both have a blog attached to it. Let's just call it firstname.lastname@example.org and email@example.com. I want my firstname.lastname@example.org account to be able to control both the blog. After you decide then open up your Dashboard (with the account that you want detach your blog from, NOT the one that you choose just now, so in my case I login using the email@example.com) and click on the Settings tab, then choose the Permission subtab.
In the Blog Author section, the one with your email address there, click 'Add Authors' then type in your other email address (I should type firstname.lastname@example.org) and hit 'Invite'. Sign out from your Dashboard. Now check your email inbox if there is a mail (from Blogger) that says you are invited to be an author, click the confirmation link and follow the given step. Usually you have to login with your other account, so that's why I told you to sign out first.
Now back to your Dashboard > Settings > Permissions (still with the account you want to detach your blog from). If you do it right, then you would see both of your email addresses, one labeled admin and one author. Beside the label you should see a link called 'make admin' and click that.
Sign out from your current account and sign in (now I sign in with email@example.com) again with your another account. Now you should be able to administer both of your blog with that one account only. You are done for this part but if you want to remove your other account (in my case I want to remove firstname.lastname@example.org from being an admin), go to your Dashboard > Settings > Permission and hit the Remove link beside your email address.
If you have any technical difficulties, feel free to comment and tell your problem, I'll be very glad to help you out.