You will need to open the file with notepad, make changes and save. The path to the file:

Disc: GamesDisciples 3.ResurrectionSystemsystem.ini

Namely:
float DamageToExpDiv = 4; // constant divisor for damage
float DamageToExpMaxLvl = 40; // maximum level
float DamageToExpMinCoef = 0.5; // value of the total exp multiplier at the minimum level (1/7)
float DamageToExpMaxCoef = 1; // value of the total exp multiplier at the maximum level

An example of the parameters I set :)
Do not forget to save the entry!