Death counter doesn't increase properly? [SOLVED]

For first, use game.Players.PlayerAdded not game.Players.ChildAdded and use player.CharacterAdded not player.Changed

remember :connect is deprecated. use :Connect

Example:

game.Players.PlayerAdded:Connect(function(player) -- Detect player join
    print("Player added")
    player.CharacterAdded:connect(function(char) -- Detect char spawned
        print("Character added")
        char.Humanoid.Died:Connect(function() -- Detect humano died
            print("Human died")
        end)
    end)
end)

Here is fixed script:

game.Players.PlayerAdded:Connect(function(player)

    -- Detect for leaderstats

    local leaderstats

    if player:FindFirstChild("leaderstats") then
        leaderstats = player.leaderstats
    else
        leaderstats = Instance.new("Folder")
        leaderstats.Name = "leaderstats"
        leaderstats.Parent = player
    end

    -- create deaths value

    local deaths = Instance.new("IntValue")
    deaths.Name = "Deaths"
    deaths.Parent = leaderstats

    -- detect character added.

    player.CharacterAdded:Connect(function(char)
    -- detect humanoid died.
        char.Humanoid.Died:Connect(function()
            deaths.Value = deaths.Value + 1 -- add 1 value to values
        end)
    end)
end)

Wiki pages:

CharacterAdded

PlayerAdded

Humanoid.Died

Hope it helped :)