Start by removing the bottom sash. We have a video on our FAQ page explaining how to do this in more detail. Release the balance as illustrated in the video (please watch carefully as this cannot easily be explained in writing). By releasing the balance, the tilt arm and shoe will automatically slide to the bottom of the chamber. Slide down the top sash and remove the top corner caps and top board. You should now be able to see the top section of the balance. By unscrewing the fixing screw as displayed you should be able to remove the balance. Insert the new balance into the chamber and fix it by screwing the screw back into the top section. Now slide up the tilt arm to allow you to attach the balance back into the shoe by pushing the balance hook in between the slot. Carefully pull down the shoe to return it to its correct position.