To improve the stability of a rocket, the Center of Pressure can be moved by:

Increasing the fin size is an effective way to move the Center of Pressure (CP) further back on a rocket, which can enhance its stability. The CP is the point where the aerodynamic forces act, and it is essential for stability in flight. By increasing the size of the fins, you generate more surface area for the air to act upon, thereby increasing the aerodynamic forces acting at the fins. As these forces increase, they help to stabilize the rocket, especially during its ascent.

This stability is crucial because it ensures that the rocket maintains a straight path and doesn’t tumble or veer off course. Larger fins provide more torque in response to any pitching or yawing motion, effectively correcting the rocket's trajectory. Therefore, the design alteration of increasing fin size is a recognized method for enhancing a rocket's overall stability and making it more effective in flight.

Other methods, like adding nose weight, might shift the Center of Gravity but not directly affect the Center of Pressure, while decreasing fin size would have the opposite effect by reducing the stabilizing force. Changing the rocket's paint color does not influence the aerodynamic characteristics of the rocket's flight, thus would not affect stability.