Here is the step by step guide on how to hard reset sony experia lt26i phone:
1.Make sure your battery life is at least 50%
2.Turn off your Sony Xperia.
3.Press and hold POWER button and VOLUME UP at the same time for several seconds.
4.release the buttons after you see the logo or android recovery.
5.Just select factory reset/wipe using volume keys then confirm using power button.
6.Just wait for the reset to be completed and the phone will reboot and will start normally.