In order to hard reset a Lenovo S939, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Lenovo S939 device will be brought back to the default configuration of a brand new device.
1. For starters, power down the device.
2. Continue by pressing and holding the Power & Volume Up buttons for a moment.
3. An Android image will appear on screen. When it does, release the aforementioned buttons and press Power button.
4. Halfway there... choose the wipe data/factory reset option - Volume buttons scroll, Power confirms.
5. Another options to select, in the same way as above, are Yes and reboot system now.
6. Your phone will now reset and restart. Voila.