How do I change administrator rights?

I have been having trouble with my computer with a message that my windows is not geniune. I could not access some things because it said I wasn’t the administrator. I found where to change that but don’t remember where that was. Now I realize it is NOT a good thing to do as it is like putting a whole in my computer for worms and viruses to enter. I would like to change it back to basic. Where do I do that?