Removing Original Admin from Used Macbook Pro

I recently purchased a used Macbook Pro from Amazon and the seller didn't remove the original Admin user, which is a Corporation and they are still managing the rights and supervising the laptop. I was able to change the password, access the laptop and create a new Admin user profile for myself. But I can't remove the original Admin. In my new profile, I don't see the original Admin. Does anyone have any suggestions for how I can remove the original Admin and remove all of their security certificates and rights?