Question

suggest one method to increase the torque without changing the magnitude of force

Answer 1

Torque can be increased in two ways:

1) by increasing the moment arm or

2) increasing the perpendicular force applied to the moment arm. The opposite is true for decreasing torque. If an object is at rest the torques on the object are balanced (they cancel out) and sum of those torques is zero.

Answer 2

Torque is directly proportional to the force applied. Basically torque is the turning moment of the force. The more you apply the force , the more will be the torque. As simple as that.

T=r*F

suppose you want to open a nut, you bring a wrench and apply force at the end of handle to open the nut. if the nut is jammed you apply even more force thereby increasing the torque on the nut and then the nut loosens.