Answer
We should decreases the magnitude of $F_2$
Work Step by Step
The torque is a maximum when the angle $\theta = 90^{\circ}$
The torque decreases to zero as the angle $\theta$ decreases to zero.
Since the angular speed is constant, the torque due to $F_1$ must be equal and opposite to the torque due to $F_2$
If $\theta$ decreases, then the torque due to $F_1$ decreases.
To maintain a constant speed, the torque due to $F_2$ must also decrease.
Therefore, we should decreases the magnitude of $F_2$
