1. Log into an account that has administrator access.
2. Then go to command prompt. There's three ways of doing it.
(1) Go to Start, Programs, Accessories, and then Command Prompt.
(2) Go to Start, Run, and then type cmd
(3) Hold the Windows Key and then press R. Then type cmd
Those are the three ways that I know of.
3. At the prompt, type net user
When you type net user, it'll list the user names. Two common user names listed are Administrator and Guest.
4. Now, to delete a user name, type in net user USERNAME /delete
Replace USERNAME with the user name you want deleted. For example, if the user name you want to delete is BILLGATES, then you would type the following:
net user BILLGATES /delete
And BILLGATES will be gone. As far as I know, this process cannot be reversed. So use it at your own risk! =)