Yep there is.
Turn on your Mac, and after the startup chime or sound,
press the command key (the one that is right next to your space bar and looks like a #) +s. This will take you to a command line, but don't panic.
Type the following: (and press enter after each line)
mount -uw /
shutdown -h now
Now, when your system reboots, you will go through the Apple Setup Assistant to setup your name info, etc. Then when you're done, go to Apple Menu>System Preferences>Accounts and delete the old admin account by clicking the minus button below the list on the left hand side.
This technique is almost common knowledge, which makes you fear for your Mac's security.
Also, in case you haven't realized, this deletes the old admin account. So, if there are files, you will have to go to Mac HD>Users>oldadminuser> and get your files.
Please let me know what you think.
And if it works for you, add to my reputation, please.