1. Make sure the tablet is fully charged.

2. Turn off the tablet. Make sure the HOLD latch is on the left.

3. Hold down Volume Up (+) button ,

4. And then Hold down Power button for a few seconds (When u press this power button the volume up button keep pressed).

5. Release Power button first, then release Volume Down (-) button.

Then you'll see the screen:
Android system recovery <3e>
Reboot system now
Apply update from external storage
Wipe data/factory reset
Wipe cache partition
Push Volume Up (+) or Down (-) to navigate to "Wipe data/factory reset",
Select "Wipe data/factory reset",

6. Confirm wipe of all user data?

Push Volume Up (+) or Down (-) to navigate to "Yes -- delete all user data",
Select "Yes -- delete all user data",

7. Then the screen shows:

“Wiping data ..
Formatting /data
Formatting /cache
Data wipe complete”

8. Then select “Reboot system now”,

And then it will reboot your tablet in next 5 minutes.During that don't press any button.