Note: Before do that take backup of your important data, phonebook, messages, images, and take out sim card and SD Card.Because after hard reset it is not possible to recover all data so it is important to take backup of all your data.
Make sure your mobile battery is charged 90% .
Turn off the mobile….
Press and hold Volume up+Volume down and power keys together.
Press volume up to enter recovery mode.
With volume down key select Recovery and press volume up to enter.
Select Wipe data/factory reset with volume up down keys then press menu button as shown below.
Press menu key again to reboot mobile.