Help with a level up script please?

Hello, Im trying to make a level script. I got the leaderboard but, how must i make that when someone gets killed it gives XP? Code:

function PlayerAdded(Player)
	local stats = Instance.new("IntValue")
	local xp = Instance.new("IntValue")
	local lvl = Instance.new("IntValue")
	lvl.Value = 1
	xp.Value = 0
	
	xp.Parent = stats
	lvl.Parent = stats
	stats.Parent = Player
	
	xp.Name = "Xp"
	lvl.Name = "Level"
	stats.Name = "leaderstats"
	
	if xp.Value == 120 and lvl.Value == 1 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 200 and lvl.Value == 2 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 320 and lvl.Value == 3 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 450 and lvl.Value == 4 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 580 and lvl.Value == 5 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 800 and lvl.Value == 6 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 1200 and lvl.Value == 7 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 1500 and lvl.Value == 8 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 1850 and lvl.Value == 9 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2005 and lvl.Value == 10 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2300 and lvl.Value == 11 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2600 and lvl.Value == 12 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2950 and lvl.Value == 13 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 3200 and lvl.Value == 14 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 3500 and lvl.Value == 15 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 3855 and lvl.Value == 16 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 4000 and lvl.Value == 17 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 4550 and lvl.Value == 18 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 4900 and lvl.Value == 19 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 5500 and lvl.Value == 20 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	end
	local maxlvl = 20
	if game.Players.LocalPlayer.stats.level > 20 then
	warn(baad)
	end
	if sbb then
		print(good)
	
elseif not sbb then
	warn(bad)
	end
end
maxlvl = 20
game.Players.PlayerAdded:connect(PlayerAdded)
sbb = game.Players.LocalPlayer:FindFirstChild("stats")
good = "A player joined and loaded succesfully!"
bad = "A player joined and haven't loaded!"
baad = "A player got more than" ..maxlvl.. "levels!"

Yeah, pretty long. I want to compress this too,

if xp.Value == 120 and lvl.Value == 1 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 200 and lvl.Value == 2 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 320 and lvl.Value == 3 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 450 and lvl.Value == 4 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 580 and lvl.Value == 5 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 800 and lvl.Value == 6 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 1200 and lvl.Value == 7 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 1500 and lvl.Value == 8 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 1850 and lvl.Value == 9 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2005 and lvl.Value == 10 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2300 and lvl.Value == 11 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2600 and lvl.Value == 12 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 2950 and lvl.Value == 13 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 3200 and lvl.Value == 14 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 3500 and lvl.Value == 15 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 3855 and lvl.Value == 16 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 4000 and lvl.Value == 17 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 4550 and lvl.Value == 18 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 4900 and lvl.Value == 19 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	elseif xp.Value == 5500 and lvl.Value == 20 then
		xp.Value = 0
		lvl.Value = lvl.Value+1
	end

But i want the max XP to increase each levels... Help please?

shortened:

local levelup={120,200,320,450,580,800,1200,1500,1850,2005,2300,2600,2950,3200,3500,3855,4000,4550,4900,5500}
game.Players.PlayerAdded:connect(function(Player)
    local stats = Instance.new("IntValue")
    local xp = Instance.new("IntValue",stats)
    xp.Name = "Xp"
    xp.Value = 0
    local lvl = Instance.new("IntValue",stats)
    lvl.Name = "Level"
    lvl.Value = 1
    stats.Parent = Player
    stats.Name = "leaderstats"
	xp.Changed:connect(function()
		if xp.Value>=levelup[lvl.Value]then
			xp.Value=xp.Value-levelup[lvl.Value]
			lvl.Value=lvl.Value+1
		end
	end)
end)

To tell when you kill someone, check if they're dead after you've done damage from the weapon. If they're dead and they weren't dead before then you killed them. Tell the server script that so it can give you xp.

If you're going to be killing npc's you can have a script that uses the semi-same technique as a linked sword and when the npc's health turns to 0 and it calls the Dead function, you can find the killer and add according XP. You can pracitcally do the same for a regular character, just do game.Players.PlayerAdded and use the Dead function to do above