Hero XP Required - Table, it's amount needed every level. Default at 200
Hero XP Gained - Creep Reduction Table, it's % of exp you gain from creep. Default is 80, 70, 60, 50, 0.. level 1 hero gain 80% xp from creep, then level 2 hero gain 70% xp from creep.. until level 5 gain 0% xp from creep. Add more value to it for more levels.
Are you looking for change hero's level cap, it's Hero Maximum Level, default at 10.