The most competitive flyers seem to like a higher pitch, but it is tricky to get work right. I use lower pitch props and get times in the same range as the best SO flyers. As an adult I don't actually compete with them so don't ultimately know if its as good.
MORE important in my mind is getting the proper MATCH between prop and rubber. Thats how I get my lower pitch prop to at least compare in performance with the guys using high pitch.
As to how to change pitch, you propably need to understand helical pitch first (see http://www.allstar.fiu.edu/aero/flight63.htm
. Then you need a pitch gauge, couldn't find one, but there are some designs out there somewhere. Finally, you have to twist the prop spar to the new pitch. Three ways I've heard of. Twist by hand till youv'e bent it permanently, takes more talent than I have. Cut and reglue, some do this successfully, I find it tricky. Apply heat to soften the shaft, twist to new position, let cool and be done. I've had most success with this.
Oh, and you can select different pitches. The different size and type of Ikara props have different pitches. I use the narrow blade prop that has a lower pitch and cut to diameter, as opposed to the wide blade prop which has a higher pitch.
You can also trim the leading or trailing edge to change pitch.
Hope that's clear