Let's pretend, first of all, that your accounts are called BloggerUno and BloggerDos. In the BloggerUno account you have two blogs, and you have one blog called "I Love Blogger" at BloggerDos. The following steps will show you how to move the single blog in BloggerDos to be with the others at BloggerUno.
First, sign in as BloggerDos and go to Settings | Members for the "I Love Blogger" blog. On the team page, you will have to send an invitation to yourself. Yes, you read that right! Click on Add Team Members at the top of the page and fill out the form with your e-mail address. Submit the form and then sign out of Blogger. Make sure you are completely signed out of Blogger before continuing.
Check your e-mail and within a few minutes of taking the steps above, you should have an e-mail inviting you to join the "I Love Blogger" blog. Click on the link in the e-mail. It will take you to the Blogger sign in page. This time, sign in as BloggerUno (this will be the opposite username from the one you were just using). Once you have signed in, you will see a link asking you to confirm your desire to join the blog. Click Join and you will be added to the blog. Once this is complete, sign out of the BloggerUno account.
When you are signed out, sign in again as BloggerDos. Go to the Team page of the "I Love Blogger" blog. You will see both of your usernames listed as being a part of the blog. Under "Admin" you will need to check both users. When both users are listed as having admin access, sign out of the BloggerDos account.
Sign in again as BloggerUno. (Yes, I know you are sighing in exhaustion at this point!) Go to the Team page of the "I Love Blogger" blog. Once again, you will see both usernames as having admin status. This time, click the "Remove" icon next to the username that you are not currently using (BloggerDos). Be very careful to select the correct one to remove, so you do not accidentally remove the current account (in which case you will have to start this process all over again).
Once these steps are complete, you will have moved your blog from one account to the other. This method can also be used to transfer ownership between two separate user individuals - you will just have to coordinate with the other person to follow the steps outlined above.