It is called "lightening" the trigger pull.
If you have to ask, you probably should not do it. But, if you are going to do it anyway, what should be done is to use a hard, natural (not carborundum) stone to polish the engaging surface without changing the geometry. Now, if you do not understand what I just said, or do not have the skill to do it, you should take it to a gunsmith instead of working on it yourself.
If you "round" the engaging surface, it will not be reliable or safe anymore.