Switch her off, then hold volume up and then press the power button. Hold both buttons until the phone vibrates and the splash screen appears. I think the option you want is wipe and delete cache.My battery is suffering since the last update, any idea what caches or something I can clear to help?
Never sure if it actually makes any difference, I do it more each update out of habit

I'm still on the fence with the latest update. I'm not sure if I've had two days out of the battery since the launch week! Average use. I think I was spoilt with my Xiaomi Note 4...