Help updating Pi-hole and the OS

I have some questions. At one point this pihole did update but stopped because of the repository and yes I have run it a long time without updating it. I had set it up as a DNS server. I don't remember how or even what I used. Is there any way you can tell me what it was?? LOL I'm old and slept many days since then. I would like to keep it as my DNS server but don't know how I would set that up again. I may have documented all of this but have no clue where it would be. Most likely I will update to the newer pihole but that isn't like when I did it before. It was an image file from pihole. Am I wrong about that?

Thank you so much for your help...