First method:
Firstly hold down the Power button, until your device is turned on.
Then from the home screen open Menu and choose Settings.
Select Backup & Reset and tap Factory data reset.
Choose Reset device and select Erase everything to begin hard reset operation.
Well done! Your tablet should restart itself right now.
......................................................................................................................................................................
Second method:
Start by swtiching off the device by pressing Power button.
Press and hold Volume Up + Power key for a couple of seconds.
You can release held keys when you see an Android Logo on the screen.
To enter the Recovery Mode hold down the Power button for a short while.
Afterwards from the menu choose "Wipe Data/Factory Reset" by using Volume buttons to scroll and Power button to select options.
Tap "yes" to confirm if you are 100% sure you want to clear all your data.
Press Power button to enter option "reboot system now".
Cogratulations! The hard reset has just been performed.