For Prop pitch, start by taking the boat out.
Get the boat on plane and trimmed out.
Get to Wide Open Throttle.
The engine should be running at between 4400- 4800 RPM.
If you're over 4800, you're under propped and need to increase pitch (or add a blade) or both.
If you're under 4400, you're over propped and need to decrease pitch. Estimate a change of about 200 RPM per inch of pitch.
You can also use the Merc prop calculator to see where it thinks you should be:
https://www.mercurymarine.com/us/en/...eller-selector
Size and pitch should be stamped on the prop hub (<Diameter> x <Pitch>)