The first thing to do is to determine your WOT rpm at the typical loading you run.
You want your prop to give you at least the lower number of the rpm range with a full load.
The boat will operate better with the rpm at the top of the range but you must be careful not to over rev it when lightly loaded.
Once you know where you are you can figure out what prop changes to make.
The difficult part with all this is getting accurate rpm readings.
For this you need an appropriate tach.
I bought this timing light for my two stroke outboards and it has a tachometer on it:
INNOVA 5568 Pro-Timing Light with Tool Case
https://www.amazon.com/dp/B000EVU8J8..._bNPWEb6AYWHTG
I didn't notice a mention of the motor being a two stroke or four stroke but it works on both.
If it is a two stroke you might also want to try this product:
Quicksilver 858080Q03 Power Tune Internal Engine Cleaner, 12oz - for 2-Stroke, 4-Stroke and Fuel-Injected Gas Engines
https://www.amazon.com/dp/B000XBFL0K..._AJPWEbTV4VARR
It clears out build up in the exhaust and lets your motor breath better.
PM sent...