While some people will argue almost violently that you can’t isolate a portion of a muscle, the fact that the pectorals have multiple attachment points allows for some variation as opposed to the biceps, which simply anchors at two end of a simple hinged joint. [Picture a fan shape for the chest, and a long-oval balloon for the bis]
You will get a lot of suggestions for incline work, either pressing or flye/cable movements. While all are worthwhile, I want to point out that in my own experience, it’s not simply a matter of where the stress is when you contract the muscles (ie. where the dumbells may be at the top of an incline press), but moreso where they return to and create the stretch.
I have found that allowing my arms to move closer to my waist at the bottom of fly and press movements, allows a much fuller stretch, and subsequent contraction in the upper chest fibers. This is especially useful if you place a low incline bench (20-30 degrees) in a cable station, and use this is a pre-exhaust movement for your pressing work.
Also, and I’ve mentioned this many times in the past, for incline pressing work, bringing the weight down to your lower chest, and then returning the weight in an arcing manner, will be hit your upper fibers much more than keeping the bar above your upper chest/collar bone throughout the entire movement.