You can change your user account name by using the command below:
wmic UserAccount where Name="OLDName" call Rename Name="NEWName"
Also You can use VBScripts To do this job, But there is a problem, When I change user account using this way, the old name is still showing on my account, but If I run "net user" command I can not see any account with my old name.
Where is the problem? Listing Accounts will show that the name is changed, but in windows from start menu I'm still seeing old account name.