You need to make sure to mount the Jack in the right place for your safety and for the longevity of the frame of the unit. Pictured below is where you want to mount the Jack to lift the side that you will be replacing the Tire on.

-Make sure your trailer is connected to your tow vehicle the whole time

• After you have your Jack mounted correctly and safely – remove the lug nuts from the Wheel and remove the old wheel then place your new Wheel on the unit. 
• You can then lower the unit and proceed to Torqueing 
• Torqueing: Using a Torque Wrench, torque the Lug Nuts on the Wheel following the specifications listed in the attachment below