A fellow boater told me I could beef up my 1977 Evinrude 115 hp to a 130 hp,by changing the carb jets is he right? if so what do I need and how do I do it?
Bob's given you some good advice . Putting oversize jets in the same carb will just overfuel the engine, causing it to run poorly. You need to be able to put more air through the engine as well as more fuel. Look for some carbs with the 1 5/16" throats.
Best way to make your motor push your boat faster is to find a lake with a slope on it and only go downhill !!!
Seriously, in reality it is usually better to get a bigger motor than change out a lot of bells and whistles that do next to nothing for you.
My 2 cents though.