How do you loggin in a computer as administrator?

If it's a Dell laptop/computer, as soon as you log in for the first time, it either automatically makes you an administrator or it asks you if you want to become one. If yours is the only account on the computer, then you can change your account from a standard user to an administrator and vice versa whenever you want to. If there's another account on your computer and they are an administrator and your not, you'll have to ask their permission if you ever wanted to do something which the computer recognises as something that needs permission, like changing your account type from standard or guest to administrator. Hope this helped! ;-)