Instructions
Make sure that your car is set to manual mode. While in "free roam" mode, go to the "Options" and tap "X." Move the cursor to "Player" and tap "X." Change "Automatic Transmission" to "Manual Transmission," then tap "X" to save your settings. Press "Triangle" to exit.
Watch the tachometer or RPM gauge. When it is nearly full, click the "Up" directional button or press up on the joystick. You will see that you are in a new gear and the tachometer reading is at the other end of the gauge.
Downshift using the "Down" directional button. When you are entering traffic or a tight curve, use the "down" arrow or press down on the joystick to go into a lower gear.