How do you log on as the computer administrator from user?

If you are using a windows based operating system then go to start menu click on switch user or Log off (if switch user button is not available directly), you will be asked to enter the name and password of your administrator account. Enter it and you will be logged on to administrator.
If you are a command line interface user on a Linux/UNIX operating system then-

* type the command $su
( here $ is a command prompt), you will be asked for the password enter the password and you are done.