Top rack of our Frigidaire GLD2250RDC3 doesn't clean well, food particles are left on glasses especially the ones placed in the back right & left corners. I have checked the spin-arms and they look clean. I always place items in the bottom rack so as not to block the water flow, and we have to put bowls in the bottom rack too because they never get clean in the top rack. We are trying to take the bottom spin-arm off but can't figure out how to do this and don't want to break anything.