832832 A14P21 MERCURY. I believe that means the prop is 14 inches across with a 21 in pitch. The pitch means if the propellor were in a solid material, such as sand you would theoretically have 21 inches of forward movement for a single, full rotation. Think of screwing a wood screw, or a the distance a machine screw would travel into a nut for a single full rotation.
The correct prop will be dictated by the combination of motor and hull. I can't answer that question directly. I would take a look at the mercury prop calculator as a start.
I would look at how the boat is performing first.
1) Find the Max RPM range for that motor.
2) Take the boat out and get it up to Wide Open Throttle (WOT). Make sure it's trimmed properly.
3) Are you in the proper RPM Range?
IF you are under the Max RPM you are overpropped.
If you are over the Max RPM range, then you are under propped.
If you are right in the Max RPM range, then it is sized ok.