Soft resets are usually conducted in an attempt to fix malfunctioning applications or because they're required for software installation.
Soft reset contrasts with hard reset, which removes all user data, settings and applications and returns a device to the same state it was in when it shipped from the factory.
1. For a start make sure your phone has unlocked screen and hold down Power Button.
2. Hold it for several seconds untill you will see this menu.
3. Now choose Reboot or Restart option from the menu and wait for your device to do all the work.
4. That's it. Your phone should run now smoother.