When a skater who is spinning extends his arms so as to double his rotational inertia then his rotation speed (rate of spin) must decrease to one-half to maintain constant angular momentum.
Similarly, when a spinning skater brings his arms closer to decrease his rotational inertia by one-half then his rotation speed must increase 2 times to maintain constant angular momentum.
For the given case, the change in the rotation speed (rate of spin) is a decrease.
