why i cannot change my stats value?

I decided to make a rank system for my games. But i cannot change the Kepintaran.Value. Is it because it is a string or something else?

game.Players.PlayerAdded:Connect(function(player)
	game.Players[player.Name]:WaitForChild("leaderstats")
	game:GetService("Players")
	local kepintaran = game.Players[player.Name].leaderstats.Kepintaran.Value
	local rank = game.Players[player.Name].leaderstats.Rank.Value
	if kepintaran >= 20 then
		 rank = "Pintar"
end
if kepintaran >= 5 then
	rank = "PelajarBaru"
	end
end)

this is my leaderstats script

local ReplicatedStorage = game:GetService("ReplicatedStorage")
	local Rebirth = ReplicatedStorage:WaitForChild("Rebirth")
	

game.Players.PlayerAdded:Connect(function(player)
	local stats = Instance.new("Folder", player)
	stats.Name = "leaderstats"
	
	local ilmu = Instance.new("IntValue", stats)
	ilmu.Name = "Ilmu"
	ilmu.Value = 0
	
	local kepintaran = Instance.new("IntValue", stats)
	kepintaran.Name = "Kepintaran"
	kepintaran.Value = 0
	
	local rank = Instance.new("StringValue", stats)
	rank.Name = "Rank"
	rank.Value = "Pemula"
	
end)

	

Rebirth.OnServerInvoke = function(player)
	local requiredIlmu = player.leaderstats.Kepintaran.Value * 15 * 2 + 15
	if player.leaderstats.Ilmu.Value >= requiredIlmu then
		player.leaderstats.Kepintaran.Value = player.leaderstats.Kepintaran.Value + 1
		player.leaderstats.Ilmu.Value = 0
		
	end
end