Lift the toilet tank lid off of the tank and set it aside. Disconnect the flapper chain from the end of the toilet tank arm. The flapper chain has a simple hook that unhooks from the arm. Place the end of the chain over the overflow tube.
Lock a pair of vise grips over the nut that secures the toilet tank arm. Hold the flush handle with one hand and turn the nut with the vise grips. If you are standing in front of the tank, turn the nut clockwise because you are looking at it in reverse. If the nut doesn't turn, the toilet tank arm needs to be cut.
Install a new blade into a utility hacksaw. These types of saws use a blade that extends beyond the frame handle of the saw. Push the saw blade between the inside of the toilet tank and the back of the handle retaining nut.
Saw through the tank arm with the utility hacksaw while bending the toilet tank arm down slightly. Avoid hitting the tank with the utility hacksaw. Once the utility hacksaw cuts through the handle, pull it away from the toilet tank then pull the tank arm piece out of the tank.