Propeller Pitch - 1985 Yamaha Outboard

I was told the pitch of the propeller can greatly affect the amount of RPMs I get with my Motor. What is the maximum RPMs I should get with the 1985 Yamaha? If I need to go up 500rpms, how much pitch do I need to increase? Is there an easy way to measure the pitch on my currect prop. I bought the Boat used and have no idea what the pitch is.

[boats.net]

Most models have a 4500-5500 rpm operating range. If you want increase rpm's drop one prop size(lower pitch) and you should gain 400-500 rpm's.