Trying to Finalize and Publish

I’ve been trying to get the website for my father’s business going after the last person had left. He gave me some simple instructions about what needed to be done, however he stopped just short of telling me everything I needed. When it came to publishing the website, I was uncertain of what to do because every page was published. I managed my way into the settings and changed it from the “demo” version of the website, which simply had the word “demo” in front of it, to the actual domain that we have for the site. When I did so it locked me out of the website and now when I try to log in to the dashboard it takes me to a completely different page. I have no idea what happened here and needed assistance.

I doubt this will be relevant, but I did also change the email address of the administrator to mine instead of the last person’s. I’m slightly frustrated at this point and am trying to gain a sense of understanding at what happened.