How to wipe a broken iphone?

I broke the screen on my iphone 5s. I want to sell it to gazelle.com. But I want to make sure all of my information is wiped off of it first just to be safe. I can't go into settings and erase all the data that way since the screen is broken so is there another way? I know when the screen is on becasue the light stll comes out a little.

1. Use Find my iPhone service
2. Change the password of your Apple ID

Gazelle is def the best way. They pay you right when they get your laptop - it's fast and convenient - I never use ebay its such a hassle. When I use gazelle, I use this link to pay me $10 more than usual.
http://gazelle.extole.com/a/clk/2528F8