1. Press and hold the power and menu key for few second untill you enter the restore menu
2. After the menu show choose “wipe data/factory reset “
3a. Select yes and your phone will be restore to default
3b. After finish choose reboot now
4. It will restart. Don’t panic because it take few minute until complete.
5. Don’t panic just wait. If there is no response in 10 minute just release your battery and put it back again and repeat from first step.
Note;
-use menu key to select.
-use volume up down to choose the menu.
-make sure u have enough power in ur batttery.
Other Method
1. go to setting~>privacy~> factory data reset.
OR
2. dial *2767*3855#
all of this method will make the same effect to your phone: -”reset your phone to factory setting”