Question about tougness on hero

I have been looking for an answer but don’t seem to be able to find it, so i hope you can help me out!

When you have a toughness card attached to your hero, and the villain attacks you, do you then simply remove the toughness card OR do you need to exhaust your hero and then remove the toughness card?

And second: can you choose wether to use your defence power (and exhaust your hero) OR to not use defence and remove the toughness card?