Access the main camera menu via the small push button on the front of the camera. You will need to hold it down for around 3 seconds.
The main Menu should come up. Go into System setting by using the push/jog wheel on the front of the camera near the menu button. Roll the wheel to select "System Setting" and then push it in to access.
Roll down to "LCD Monitor" and select this item, in here you will see "Aspect Conv", select "LTBOX".
Be aware though that depending upon the down conversion settings in the SYSTEM MODE menu you may effect the SDI output on the rear/side of the camera.