Some of the characteristics of African American nasal skin are increased thickness and increased fatty content, especially at the tip. The base of the nose can also be quite wide with flaring of the nostrils.
It is not easy to adjust all these areas without extensive surgery because the skin can prevent a lot of detail from showing through. The trap you want to avoid falling into is going overboard with your expectations. You can't make a Caucasian nose out of an African American nose no matter how hard you try, so don't go down that road.
It is possible to narrow and adjust the height of the bridge. It is possible to narrow the tip somewhat and give it more projection. It is possible to narrow the width of the base of the nose and even decrease the diameter of the nostrils, but you will look different and need to be O.K. with that.
My suggestion is to go see a specialist in rhinoplasty and have them perform some computer simulations with you to get an idea of how you would like your nose to look. Remember, with a computer you can make a nose look like anything. The simulation is not a guarantee or warranty of outcome, only a tool for your surgeon to determine your aesthetic goals. What you want to happen may not even be possible.