Here's a good tip for you: Whenever you're looking for something in the Options dialog, you can search for it right there in the dialog. There's a search box at the lower left. Type in a word or two and it will show you were it is in Options. If what you're typing doesn't exist, this doesn't help. But in this case, it helps a lot because you know exactly what you're looking for.
In fact, I'm not going to tell you where it is. Because now you can find it very easily by yourself.

Come back and ask again if you can't find it for some strange reason. Good luck!
Brian.