Enter your existing combination by pressing down the correct numbered buttons. Slide the "Open" switch downward.
Lift the door off the Supra safe.
Pry the plastic cover off the back of the door. A set of numbered screws with arrows are revealed.
Notice how the the arrows on numbered screws point left or right. Numbers not in your combination point to the left.
Use the screwdriver shaped tip on the plastic cover removed in Step 3 to turn the screws.
Move the numbers that will not be in your combination so the screws point left. Numbers used in your combination should point right.
Test your code while the Supra safe is open. Punch in your code then try sliding the "Open" switch. It will only move halfway if you entered the wrong code.
Install the plastic back over the screws and replace the door. Your new code is ready for use.