Courtesy of CheatCodes.Fartoo.com
To get better stats, every time you must first sign a contract for a fight.
Then, chose to train aggressive. Then choose either balance, power, or speed.
Then, continue. The game will show your boxer before, and his stats
either going down or up. If they go up, fine. If they start to go down,
press Home to return to the PSP's main screen. Go back into the game, and do
the same thing again, looking for better stats.
Note: The only reason this is useful is because the game loads fast.