i found this online, however i cant check it as i only have 1 domain user account on my windows 7 machine.. worth a punt though. you may need to log in as the admin account first though probably?
1. Click Start and click Control Panel.
2. Open User Accounts.
3. Click the Change your account name option. If you want to rename another user account, click the Manage another account option and select the account you want to rename.
4. Type in the new account name within the New account name field.
5. Click the Change Name button.
That's what he's already done but it's left the users Profiles and User Documents named as previous.
There isn't an easy way of doing this but if you login as admin, run up RegEdit and then locate the following key in the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
Within this key locate the entry for the user you want to rename, then alter ProfileImagePath so that it's correct.
Then highlight
HKEY_USERS
then within the File menu select Load Hive, then browse to C:\Users locate the user folder and within that select the file NTUSER.DAT, give it a name when prompted.
Now within
HKEY_USERS\<name that you gave>\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders
and
HKEY_USERS\<name that you gave>\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
Find all occurrences of the previous name and change.
When you finished the above highlight
HKEY_USERS\<name that you gave>
and from the File menu select Unload Hive
Now rename the actual folder that's incorrect, I normally then do a reboot and then login as the user and hope
Or you could do as pointed out above, make a backup of all the important files/folders, delete the incorrectly named folder, delete and re-create the user, then login and finally do a restore of the files backed up.