How to make a variable control a number in script? Options

[HeartBorne]

Hey guys
The subject is pretty much self explanatory.

I have this line to control the difficulty of the battle system i use:

@ai_level = 2

How can I make a variable control that number?
I've tried some things but none worked, anyone can help?

[HeartBorne]

thanks for your help but I still can't get it right...
Maybe its because ai_level can't be set to 0? IF that's the case could it be something like ai_level = variable + 1 ?

I am trying to do it on Gubid's tactical battle system (GTBS) if anyone has heard of it...

It uses

class Game_System
attr_accessor :ai_level

earlier in the script along with some other stuff and then:

alias gtbs_GS_init initialize
def initialize
@ai_level = 3
end

and much lower it returns with

def ai_level
return $game_system.ai_level
end

Am I doing something wrong?