How do I reset computer and Administrative settings?

[yamarider18]

Okay, so here is how my question comes about... I have already searched and could not find links to other threads..

I bought a G4 desktop from a guy on craigslist about a week ago and I want to upgrade from 10.3.9 to the newer 10.5. He has an administrative account on the computer and whenever I try and load the 10.5, it asks for his password. I called the guy wondering what his password was and he told me. I tried entering that in and it will not work. Now the guy will not answer his phone or his e-mail address. I know he was the original owner because of the information on the computer and the name on the business card he exchanged for mine.

I would really like to upgrade my OS but I need to know how to go about reseting the computer to erase 100% of everything on the computer. Can someone please help me, I am new to Mac and I don't really know what to do!!!

 

[BlueRevolution]

Insert the 10.5 disk, then restart the computer holding the C key from when the startup sound goes to when the Apple logo appears. When prompted, choose to erase and install.

 

[JediMeister]

2 ways to do this. You can follow the steps on here to reset the computer administrator password, and then create yourself a new user with admin rights. Delete the original user and all the applications will still be on the computer but the seller's data files will all be gone. Then install 10.5. Assuming the seller didn't have a firmware password, you can stick in the disc, and rather than starting the installer from there, just restart the computer, hold down 'C' (until a gray screen with the Apple logo and a spinning gear) to access the Leopard install disc. This will bypass the need to enter a password. From there go through the setup of the installer and on the Select a Destination screen, pick the internal drive, then click Options to pick Erase & Install. Note that a stand-alone Leopard retail disc does NOT include iLife.

 

[BlueRevolution]

Whenever I buy a new used computer, I always format it completely. You never know what the seller may have left behind.