Step:

1. First of all, turn your cell phone off by using the Power key.
2. then you should press and hold Volume Down + Power button at the same time for several seconds.
3. You should release held keys when you see an Android Image in front of you.
4. Now hold down the Home button to enter the Recovery Mode.
5. Use Volume buttons to select "wipe data/factory reset" and tap the Power button to confirm.
6. Then choose "yes" from the menu, and accept it with Power button.
7. then  select "reboot system now" using Power button.
8. Enjoy life!.