Q: Delete console code

Because my Imac was hacked, I'm worried that the information on the console is still viewable by the hacker. I would like to delete if possible. I believe that they can still remotely log onto my mac. I pinged my IP address and it wasn't at my location. Concerned. Also IP address within the console coding is an IP at Southern California University's think tank school. Concerned. I don't know what more to add. Need help to go further on request.