See it here How to rename or move a User Profile folder?
[WARNING: Changing the Windows user’s folder may stop your current application from working properly!!!]
- Log in as another administrator user other than the one need to rename.
- Go to C:\Users\<Your current user name>, rename it to the new name.
- Start – Right click “My Computer” – Manage – User and Group.
- Select you username and change it to the new name.
- Open registry (Start – Run – regedit)
- Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
- Go to the SID which has the “ProfileImagePath” value as your current user name.
- Change it to the new name.
(Be sure to back up your registry first)