But my opinion is that if your case goes smoothly, it is hard for you to cancel the current contract without obvious breachment from your attorney. What are the consequences listed in your contact if you break the agreement? Think about the consequesnce before you take an action.
However, if you get RFE for your 140 or 485, then you may terminate the service from your current attorney via a written notice and keep copies of all your documents and correspondence with your attorney just in case they want to mak trouble to you.
Just for reference!!