Unfortunately, you cannot change the name of a C:\Users\(user-name)
user folder. The only way around this is to create a new account of the same type (ex: administrator), then copy all of the contents from the old account's C:\Users\(user-name)
user folders (including hidden AppData
folder) into the corresponding new account's C:\Users\(user-name)
user folders. After everything checks out ok, you can then delete the old account from while logged in the new account.
Hope this helps,