SQL 2012 :: Migrating Database To New Server - Map Login To Users

I am migrating a database TESTDB from SQL 2008R2 to a new server running SQL Server 2012.

Management has decided the current sql users should have "better" user names. So the login and username "BadUsername" on the old server should be called "GoodUserName". Goodusername should have the same permissions as Badusername.

I have now restored a backup from the old server to the new server.

I used the following script for creating the login:

CREATE LOGIN [GoodUserName] WITH PASSWORD=N'difficultpassword', DEFAULT_DATABASE=[master], DEFAULT_LANGUAGE=[us_english], CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF
GO

Then I run the following script:

ALTER USER Badusername WITH LOGIN = GoodUserName, NAME = GoodUserName

But the results are not what I wanted. I now have two database users: Badusername and GoodUserName. I would have preferred if BadUserName was "replaced" by GoodUserName, but it won't be a problem if I have to delete badusername manually. Worser is that GoodUserName have NOT "inherited" any permissions from Badusername.

Is there an easy way to transfer permissions or do I need to loop through the permissions of badusername and apply those to badusername?