- Check that your phone is on.

- Next from the Home screen press Menu -> Settings -> Backup & reset -> Reset device -> Erase everything.
- Confirm your choice, and wait to finich operation.
- That's all.
Second method:
- Press Power button, until your tablet is off.

- Now press and hold together: Volume Up + Home button + Power button, until you see Recovery mode.

- Then select "wipe data / factory reset" using Volume buttons to navigate and Power button to confirm operation.

- Next choose option "Yes -- delete all user data".

- After that confirm option "reboot system now".

- Well done