i need help with a health system ?

i wont the players health to go by 50 for every lvl up the player gets

game.Players.PlayerAdded:Connect(function(player)
	script.Parent.Humanoid.MaxHealth = 50 * player:WaitForChild('Stats').Level.Value  -- this is max health
	script.Parent.Humanoid.Health = 10 * player:WaitForChild('Stats').Level.Value -- this will be how much health when player join
end)

something like this?

player.Stats.Level.Changed:Connect(function(player)
    player.Character.Humanoid.MaxHealth = player.Character.Humanoid.MaxHealth + 50
end)

this is my stats code

local DataStore = game:GetService("DataStoreService")

local Data_Key = 0

local Level_Data = DataStore:GetDataStore("Level"..Data_Key)
local Exp_Data = DataStore:GetDataStore("Exp"..Data_Key)
local Strength_Data = DataStore:GetDataStore("Strength"..Data_Key)
local Defense_Data = DataStore:GetDataStore("Defense"..Data_Key)
local Stamina_Data = DataStore:GetDataStore("Stamina"..Data_Key)
local DevilFruit_Data = DataStore:GetDataStore("DevilFruit"..Data_Key)
local DevilFruit_Owned_Data = DataStore:GetDataStore("Owned_DevilFruit"..Data_Key)
local SkillPoint_Data = DataStore:GetDataStore("SkillPoint"..Data_Key)

local Start_Level = 1

game.Players.PlayerAdded:Connect(function(Player)
	local UserId = Player.UserId
	
	local Stats_Folder = Instance.new("Folder",Player)
	Stats_Folder.Name = "Stats"
	
	local Level = Instance.new("IntValue",Stats_Folder)
	Level.Name = "Level"
	Level.Value = Level_Data:GetAsync(UserId) or Start_Level
	
	local Exp = Instance.new("IntValue",Stats_Folder)
	Exp.Name = "Exp"
	Exp.Value = Exp_Data:GetAsync(UserId) or 0
	
	Exp.Changed:Connect(function()
		if Exp.Value >= 500*Level.Value then
			Exp.Value = 0
			Level.Value = Level.Value+1
		end
	end)
	
	local Str_Stats = Instance.new("IntValue",Stats_Folder)
	Str_Stats.Name = "Strength"
	Str_Stats.Value = Strength_Data:GetAsync(UserId) or 0
	local Def_Stats = Instance.new("IntValue",Stats_Folder)
	Def_Stats.Name = "Defense"
	Def_Stats.Value = Defense_Data:GetAsync(UserId) or 0
	local Stamina_Stats = Instance.new("IntValue",Stats_Folder)
	Stamina_Stats.Name = "Stamina"
	Stamina_Stats.Value = Stamina_Data:GetAsync(UserId) or 0
	local DF_Stats = Instance.new("IntValue",Stats_Folder)
	DF_Stats.Name = "DF"
	DF_Stats.Value = DevilFruit_Data:GetAsync(UserId) or 0
	
	local Skill_Point_Stats = Instance.new("IntValue",Stats_Folder)
	Skill_Point_Stats.Name = "SkillPoint"
	Skill_Point_Stats.Value = SkillPoint_Data:GetAsync(UserId) or 0
	
	local DF_Owned = Instance.new("StringValue",Stats_Folder)
	DF_Owned.Name = "DF_Owned"
	DF_Owned.Value = DevilFruit_Owned_Data:GetAsync(UserId) or "None"
end)

game.Players.PlayerRemoving:Connect(function(Player)
	local UserId = Player.UserId
	
	local Stats_Folder = Player:WaitForChild("Stats")
	local Level = Stats_Folder:WaitForChild("Level")
	local Exp = Stats_Folder:WaitForChild("Exp")
	local Strength = Stats_Folder:WaitForChild("Strength")
	local Defense = Stats_Folder:WaitForChild("Defense")
	local Stamina = Stats_Folder:WaitForChild("Stamina")
	local DF_Stats = Stats_Folder:WaitForChild("DF")
	local DF_Owned = Stats_Folder:WaitForChild("DF_Owned")
	local Skill_Point = Stats_Folder:WaitForChild("SkillPoint")
	
	Level_Data:SetAsync(UserId,Level.Value)
	Exp_Data:SetAsync(UserId,Exp.Value)
	Strength_Data:SetAsync(UserId,Strength.Value)
	Defense_Data:SetAsync(UserId,Defense.Value)
	Stamina_Data:SetAsync(UserId,Stamina.Value)
	DevilFruit_Data:SetAsync(UserId,DF_Stats.Value)
	DevilFruit_Owned_Data:SetAsync(UserId,DF_Owned.Value)
	SkillPoint_Data:SetAsync(UserId,Skill_Point.Value)
end)

So you have a few issues. A big one being you're not using datastores, if you don't know what those are, they're what saves your player data so when they leave and rejoin, all of their money/health/level doesn't get set to 0. Heres a useful video to learn about datastores: youtube.com/watch?v=DkYupSBUpes

I'm not going to teach you about datastores, but I will tell you how to make the players health increment.

Another small thing is that you're not using variables, which bugs me a little bit.

1. Add a RemoteEvent in ReplicatedStorage

2. Add the script into ServerScriptService

3. Add the local script into StarterPlayer>StarterPlayerScripts

Script in ServerScriptService

-- Gets the remoteEvent.
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local remoteEvent = ReplicatedStorage:WaitForChild("remoteEvent")

-- Sets the data.
game.Players.PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function(character)
		remoteEvent.OnServerEvent:Connect(function(player, level)
			local humanoid = character:WaitForChild("Humanoid")
			local moneyPerLevel = 50 -- Variable incase you want the players health to go up by more than 50.
			
			local function update() -- Made a function in case if you want other things to happen when they level up.
				humanoid.MaxHealth = moneyPerLevel * level
			end
			
			update()
			print("Players MaxHealth: "..humanoid.MaxHealth) -- Debugging...
		end)
	end)
end)

Above, is the setter. Like its name, it will set the data. Meaning, it changes the health to what it is supposed to be at.

Local Script in StarterPlayer>StarterPlayerScripts

local player = game.Players.LocalPlayer

-- Gets the remoteEvent.
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local remoteEvent = ReplicatedStorage:WaitForChild("remoteEvent")

-- Gets the level.
local statsFolder = player:WaitForChild("Stats", 100)

local level = statsFolder:WaitForChild("Level")

-- Fires it so the data doesn't equal 0.
remoteEvent:FireServer(level.Value)

-- Checks if the value changed, if so, fire the remoteEvent.
level.Changed:Connect(function()
	remoteEvent:FireServer(level.Value)
end)

Above is the getter. I don't think I need to explain how this works, it's just the opposite of the Script...

I hope this helped you, if it did, please mark this as the accepted answer to help other people. If you have any questions then comment!

ALSO: I recommended renaming your stats folder from Stats, to leaderstats. So you can use the built-in Roblox leaderboard...