Well you couldnt exactly change the amount of troops in a fight, it all depends on the morale your team has, the chance of you winning the fight, and the tactics level you have (which also helps out alot in increasing the amount of troops you have in a fight). Overall you would just need a better skillset and more troops to fight with on your ship in general as well as 'Excelent' morale

In options (must be in-game rather than through the configuration client), there is a slider to change battle size, which I think is what you're looking for. It controls the amount of maximum units that can enter a battle at any time (rather than having a certain amount of units total and sending in reinforcements as those troops die/are knocked out). Also, are you referring to the assassination attempt battles or the infested village battles?

Both types of battle I see a zerg of Enemies then my Game crashes