After installing an Operating System generally we use the computer as an Administrator. But you can rename Administrator. Suppose your name is Pritom and you want to replace Administrator by your name Pritom. To do this you have to right click on My Computer and then click on Manage. Then a box will be seen like this..........   Now double click on Local Users and Groups. Then the box will appear like this.   Now double click on Users and you will get Options like these.   Now double click on Administrator and then click on Rename. Now rename this and Restrat your PC(Computer).