The battery on my 4S dies in few hours. How do I shut it off completely to then restore from ICloud?

The battery on my I4S has suddenly started dieing in just a few hours. Previously it held charge for entire day. I have turned off all apps, bluetooth, wifi, and everything I can without changing the battery life. I was told to "hard" reset the phone. How do I completely shut the phone down and have it reload from ICloud?