Hard Reset BENQ B50

First method:

Power off the cell phone by pressing the Power button for a short while.
Then press and hold Volume Up + Power at the same time for a few seconds.
You can release held keys when you see an Android icon.
Use Volume buttons to select "wipe data/factory reset" and tap the Power button to confirm.
Afterwards choose "yes" from the menu, and accept it with Power button.
When the Recovery Mode appears again on the screen select "reboot system now" by using Power button.
Well done! The hard reset has just been performed.