Depending on what year and what stereo package u got all u may need to do is grab an amp. On the lesser optioned Axis boats there is no amp on the speakers. They are wired directly to the head unit. So just adding an amp will boost your stock speakers. I believe they are Alpines correct? They are a pretty decent middle road speaker. If you do have an amp make sure the settings are all good. Like gains, crossovers, frequencies .
Boat mfg just throw stereo gear in their boats. Really never set it up to optimize the sounds.
First things first. Post exacy what you have model wise speakers and amp if there is one. Then we can give you much better advice. You build a system from the ground up. So lets make sure what you ready have is installed correctly before we start gutting it