that's pitch, the 12 and 14" are pitch, both have similar diameter.
So with a 14" pitch your top speed will be higher (more distance covered for same RPM) but acceleration slightly slower. Going to a 12" pitch you will have better acceleration but lower top end, assuming you are getting correct WOT (Wide Open Throttle) RPM.
Generally for heavier boats you want more diameter and less pitch, lighter boats require less diameter and can plane with higher pitch props.
Unless you are unhappy with the performance just now then go for a replacement of the same prop. There's a 13" pitch on gumtree just now - https://www.gumtree.com/p/boats-kaya...rd-/1170051087