Picture A 
 
Step  3:  In  this  menu,  power  button  =  Enter  key,  volume 
button = up and down key.   
Press  volume  button  move  to  line  5  "wipe  data/factory 
reset", and press power button to confirm. 
At this time, come to the next  menu shown as following 
picture B, press volume button move to the line with "Yes", 
press power button to confirm.