CAUTION: Do not use this process if you have a Managed Account. Contact your system administrator for support.
NOTE: This process results in the creation of a new account and migration of your user data to that new account. The new account may not have access to data from the old account on any other system such as cloned hard drives or Time Machine backups.
Apple's support article HT1428: OS X: How to change user account name or home directory name, has been updated to be very similar to this User Tip and I can now recommend it. Please see the version history if you want to see my old versions.