go to System Preferences > Accounts > from your account place a tick on Allow user to administer this computer IF the lock icon is open, otherwise you will need the admin user name and password to unlock it. If you don't, then you will need to change the admin password with the Install Disks.
Changing your administrator password
To change the administrator password, you must know the current administrator password. If you're logged in as the administrator, open Account preferences and click the Change Password button.
If you don't remember the password and automatic login is turned off, you can reset the administrator password using the Mac OS X User Install disc.
IMPORTANT: Because a user with the Mac OS X install disc can gain unrestricted access to your computer, you should keep the disc in a safe place.
To reset the administrator password using the Mac OS X disc:
Insert the Mac OS X Install disc and restart the computer.
When you hear the startup tone, hold down the C key until you see the spinning gear.
When the Installer appears, choose Utilities > Reset Password.
Follow the onscreen instructions to change the password.
Quit the Installer and restart your computer while holding down the mouse button to eject the disc.
Be sure to change your login password in Keychain Access to match your new password.