First method:
Power off/ Switch off your mobile.
After that press and hold Volume Up + Volume Down + Power button until you see menu.
Next, choose option Recovery from menu using Volume Down to navigate, and Volume Up.
Note : If Volume Up button doesn’t work, then use Power button to select.
Now you will see yellow triangle and Android mobile logo.
Then press Volume Down + Volume Up to see menu.
Please use Volume buttons to select option “wipe data / factory reset”, and confirm that using Power button.
Select option “Yes — delete all user data”. from list.
After that accept “reboot system now”.