Maximising DC motor torque within parameters - and stuck on terminology
A DC motor has a torque constant.  That means that it will give you some amount of torque per ampere that you supply to the motor.  

You can trade RPM for torque with a gearbox, so the torque increases with decreasing RPM while the power for a fixed load stays constant minus gearbox losses.

You can get a different motor with a different torque constant, but bottom line is angular velocity times torque = power, and the power you have available is dependent on your power supply and the losses in your controller.

If you need more torque at the same RPM you need to supply more power.If the motor isn't rated for the additional power/current you need a different motor.