Level gui system help?

Long story short, im making a game where theres a level up system based on kills and I use the script

local maxlevel = 100
game.Players.PlayerAdded:connect(function(player)
    local stats = Instance.new("IntValue", player)
    stats.Name = "leaderstats"

    local level = Instance.new("IntValue", stats)
    level.Name = "Level"
    level.Value = 1

    local exp = Instance.new("IntValue", stats)
    exp.Name = "Exp"
    exp.Value = 0

    while wait() do
        local extralevel = level.Value
        local expneed = ((extralevel * 2) - 1) * 50
        if level.Value < maxlevel then
            if exp.Value >= expneed then
                level.Value = level.Value + 1
                exp.Value = exp.Value - expneed
            end
        end
    end
end)

2 questions: 1, I made a working gui version of displaying the level, HOWEVER it wont update when you level up it works the first time but wont no more, help, to go along with the leveling up. 2, Using this script how would I make it so if you kill someone you get exp?