How to reset an iphone to factory defaults without using the touch screen?

How to reset an iphone to factory defaults without using the touch screen?

Added (1). * The reason for this is that I've smashed the screen to the point that it's unusable. I'm going to sell it on ebay but I'd rather clear everything on it first. Model: 5c

Edit two: When trying to do this through Itunes, it asks me to go onto settings and disable find my iphone before I can restore, which obviously I can't do.