If you remove the upper from your rifle you can hold the hammer with your left thumb and press the trigger. Slowly let the hammer go all the way forward till it stops, NEVER let it fly forward on its own, it 'shouldn't' matter if you do it accidentally once or twice
But repeated hammer falls can damage, if not crack the plastic of the lower or in extreme cases break the hammer itself.
Anyway once the hammer is all the way forward, look down on the rear side of the hammer by the pivot pin and you should be able to see a small shiny flat spot.
That is the hammers bearing surface, its half of the polishing equation. The other half is the bearing surface at the front of the trigger assembly. You can't see it without removing the trigger because it's underneath the hammer and its pivot pin.
To do a really proper polishing job on them you really do have to take the hammer and trigger out of the lower.
Just be VERY careful that you do not change the shape or angle of these surfaces or you could easily make a mess of things.
If you have never done anything like this, you can still do a credible job of it by just putting some polishing compound on the hammers bearing surface and just sit down and continually using your thumb to cock the hammer and pulling the trigger.
Replace the compound every 5 to 10 minutes while you watch TV for a night or two and you should have a decent trigger feel.
After a night or two doing that make sure you thoroughly clean the lower out to remove any residual compound and you should be able to feel a much smoother if not lighter trigger pull.