take a soft cloth & fold it several times to reach the right thickness and a large screwdriver or even a jack handle and lever one side carefully/barely until it starts to move off of the threads then move 180 over & repeat til it breaks loose so it comes up/off straight w o cocking and if it has a little lock tab over the bottom side of the threads to keep the arm from coming off of the threaded post move it out 1st before you start levering anything so the arm is free to come off unobstructed