Is it fed off a security panel? Kill and remove that first
If it's on a breaker in your main panel, remove it before anything else
Test with an actual voltage meter if possible
If any of this sounds like it might be above your pay grade, an electrician can probably safely demo the whole thing in a couple hours. It shouldn't cost an arm and a leg, maybe a few hundred If you go to a small company like mine (little one-man deal, should be plenty of good ones on Angi that are vetted).
Edit: forgot this was DIY for a second, sorry if this violates any rules. I'm an electrician by trade. To be honest, electrical, plumbing, and hvac should be left to professionals in my opinion. Electricity is an invisible death force that starts fires in your sleep. Don't mess with it if you're not really solid with the work.