By default, if there is only one user on the Mac, that account has Admin rights.
Is it possible that you are not using the correct password and not that you don't have admin rights.
Take a look at the Accounts pane in System prefs and check that there is a check mark next to the option to "allow this user to administer this computer"
Let us know. If there is not, and you cannot get a check mark in there, let us know. It is possible to reset all the passwords.
P
Somehow I do not seem to be recorded as Administrator on my MacBook Pro .All I seem to have is a Usert Name and a Password - which are not accepted when I want to make certain changes. I have no idea how this came about. I would be most grateful for advice as to how I may create myself (the only User!) as Administrator.

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