Actually you don't.
On an incline press the weak links will ALWAYS fail before the chest (unless pre-fatigue or a similar technique is applied). Shoulders and triceps are the weak links, putting the bench on an incline will bring the shoulders more into play, and put the chest in its weakest position. The pec majors primary function is to pull the arm across the chest and downward - therefore a decline press/dips are the best among the presses. A dip/decline press will minimize the weak links (the lats will come into play more, but they are not a "weak" link and act only as a stabilizer), and put the chest in its strongest position.
Don't buy into that "you can work the upper chest with incline presses and the lower with declines!" crap. This is not possible because of the pecs anatomy. Period.
In case you don't get the point - you should work the chest in its strongest position and minimize the weak links, and do not waste time trying to target the upper/lower chest individually.