Here is a video link on iGrow 800 Setting Up Password Protection

To get to the Password setup screen, from the home screen you would hit OK->System Setup->Password (button#7) 

To set a password hit button #7, once the banner pops up "Add Password." Hit OK and you will be prompt to enter a password, once entered, hit OK, and simply hit HOME to save your changes.

Once a password is set, to remove the password, user needs to go to password option and use Wheel to disable (remove) the password.

 Note:

If button #7 Password is disabled it will display Password (disabled) with only 1 option, to add a password.

If button #7 Password is enabled it will display Password (enabled) with 2 options, to edit or remove password.

The way the Password protect works is that once you set the password, and the controller is idle for 15minutes, without anyone touching it, it goes into password protect mode and if you try to hit any button to enter or change programming the Password screen pops up requiring a password to proceed.