Have a poke around in Combatassistant.java should be bluntly obvious when you stumble across it, but for my source Its....
Code:
int damage = Misc.random(c.MAGIC_SPELLS[c.oldSpellId][6]);
So you could try something like,
Code:
int damage = Misc.random(c.MAGIC_SPELLS[c.oldSpellId][6])+5;
But you should have good reasoning why you'd want to do this as it will unbalance your server greatly in terms of PvP and such, IMO just leave it how it is unless your combat system is truely messed up in which case you should probably rip a better one.