A soft reset (turning the device off then back on) is similar to restarting a desktop computer and is one of the first steps in troubleshooting a device. In most cases, a soft reset won't affect data on the device, unless the battery is very low.
Press and hold the Power/Call button.
A voice message plays the time then says "Turning off now, goodbye". Release the call button.
Press and hold the Power/Call button for 4 seconds to power the device back on.