What should I do to get that "divided -chest",particularly UPPER CHEST?

To develop your upper chest you must learn to attack from different angles. Put your feet on a step, or incline of some sort and do push ups that way. You can also do Incline bench press which may feel a lot heavier than a regular bench press, or a decline bench press that may feel lighter than a regular bench press. Just remember to keep your body guessing with what you throw at it.