I feel your pain, My boat was new to me this year and the steering was hard to turn. I regreased it in a few places and it got a bit easier but still noticably hard. What helped the most was just using it - once I started using the thing and put some miles on the boat, it loosened up enough so my kids could turn it.
One test to do is disconnect the steering from the motor, where it meets the motor. If the motor turns pretty easily by hand (considering the weight of the engine) then the problem is in the wheel, cable, or cylinder. If the motor itself is still hard to move, then it the motor mount(whatever you call it) needs more/new grease. I think mine could use a new cable myself.
At least that will get you diagnosing which side of the connection to look at.
Will