2 to 1 nap transitioning

Our 14 months is experiencing a 2 to 1 Nap transitioning right now, everything’s fine except his total sleep time dropped (used to be 13.5 hrs and now down to 12.5 hrs), and his wake window is too long (6hours for the 2nd wake window) and sometimes he gets overtired and extremely cranky. Just wondering what are the best way to help him to make the transition smoother?