1. Charge the battery 100 percent.
2.Turn off your Karbonn Android phone.
3.Turn ON the device by pressing and holding the VOLUME UP key and the Power key together.
4. When Android system recovery menu appears, release VOLUME key.
5. Select wipe data/Factory reset using volume key.
6. Select with Power or Cancel using Back key.
7. Hard reset is done switch ON the mobile.
Karbonn A51 have following features:-
•Android Ice Cream Sandwich OS v4.0
•3.5-inch Capacitive Touch screen
•3.2 MP Rear Camera