One option is to set up a new user 'admin' account (back up everything from your Home Directory first).
Go to System Preferences/Accounts/Login Option. You'll need to authenticate with your Administrator password.
Click the '+' button to create a new user account.
Select Administrator from the drop down menu. Complete the boxes as requested.
Ensure you fill in your .Mac account name if you own such an account.
Then log out. When you log back in, choose your new administrator account.
Once logged in, go to System Preferences/Accounts/Login Option and delete your old admin account.
You will then have to reset any desktop preferences (e..g desktop picture, screen resolution etc).
Copy over files from your back up to your new user account.
Mac Mini 1.83GHz 2GB 10.7.5
Macbook Pro 2.53GHz 4GB 10.8.2
"The past is a foreign country: they do things differently there." L. P. Hartley, British novelist 1895 – 1972