Source: http://superuser.com

1. Create a local user account with administrative privileges if you don't have one already.

2. Reboot.

3. Login with local account with administrative privileges.

4. Win+X, G (Computer Management) → System Tools → Local Users and Groups →Users, right-click user, Rename.

5. Win+X, A (Command Prompt (Admin))

   ren C:\Users\dzinx_000 dzinx
   

6. Win+X, R (Run)

   regedit
   

7. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList\ and find the SID for your user account. You can simply open each folder and check the ProfileImagePath for the correct one.

   Rename the ProfileImagePath value to your desired name, like C:\Users\dzinx

8. Log in with your Microsoft account. Everything should work fine: