According to Newton's 2nd law, acceleration is directly proportional to the net force acting on an object and inversely proportional to its mass. This is expressed by the formula \( F = ma \), where \( F \) is the net force, \( m \) is the mass, and \( a \) is the acceleration.
To increase the acceleration of an object, you can:
- Increase the force acting on it (while keeping mass constant).
- Decrease its mass (while keeping force constant).
Therefore, the correct answer is B: decrease its mass and increase the force acting on it.