increasing the velocity of a projectile object.

I have a ball and once i release the mouse button the ball moves in a projectile motion. I want my ball to move faster but the trajectory should remain same

xAngle = 45f;
yAngle = 45f;

void Update ()
{

if(Input.GetMouseButtonUp(0))

{

   ball.AddRelativeForce(xAngle, yAngle , yAngle * 1.5f);

}

}

You can handle it a couple of different ways. You can add a small amount of force every frame. Assuming the script was on the ball:

rigidbody.AddRelativeForce(Vector3.forward * factor * Time.deltaTime);

Or you use the ConstantForce component (Component/Physics/Constant Force).