Disconnect the end of the steering cable from the steering link on the motor. Swing the motor from side to side - It should be very easy. If it does swing easy, turn the steering wheel lock to lock and it should be easy also.
You could do some greasing - there is probably a Zerk to lube the steering swivel and grease the cable through the tilt tube. There two places to start before buying parts.
If the steering is still stiff after greasing and the motor swings easy, it is probably time for a new cable or a replacement steering system, including the helm. Often a kit with a helm and cable is only a few bucks more than the cable by it self. iboats carries kits and cables.