help? im having trouble converting this Grab Knife into r15? Nothing happens when ading "Upper"?

I have this Grab knife, and using the roblox wiki info, it said to change all Torso and right arm to upper. But this is no ordinary knife, you can grab humanoids. but nothing happens when i turn everything to upper. it wont even weld to the hip, it wont do anything but display in the backpack. Why is this not working, what all do i need to change to make it work for r15. It is currently for r6, so the main question is, why is it not work when i change everything to "Upper'? What all do i need to change to make it work for r15? also if you happen to be in studio type up " Grab knife V3" and try it with r15 you will see, then try with r6. Thank for helping. here the script i am trying to change.

math.randomseed(tick()) local player = game.Players.LocalPlayer local rekt = {} local paralyzed = false local curpoint = nil local curpart = nil local finishnum = 1 local zombiemode = false local zombies = {} local lastgui = nil local mouse = player:GetMouse()

function getplr(char) local plr = nil for i,v in pairs(game.Players:GetChildren()) do if v.Character == char then plr = v end end return plr end

function bleed(frick) while frick.Parent ~= nil do local reeee = coroutine.wrap(function() local thing = Instance.new('Part',game.Workspace) thing.Size = Vector3.new(0.2,0.2,0.2) thing.CFrame = frick.CFrame thing.Shape = Enum.PartType.Ball thing.CFrame = frick.CFrame thing.Transparency = 1 thing.BrickColor = BrickColor.new('Maroon') thing.Material = Enum.Material.SmoothPlastic thing.Name = "Blood" thing.CanCollide =false local rawrxd = Instance.new('BodyForce',thing) rawrxd.Force = frick.CFrame.upVector*(math.random()*2)+Vector3.new(math.random(-5, 5)/10,1.5,0) local coru = coroutine.wrap(function() wait(0.01) rawrxd:Destroy() end) coru() local ree = Instance.new('ParticleEmitter',thing) ree.Color = ColorSequence.new({ColorSequenceKeypoint.new(0,Color3.fromRGB(100,0,0)),ColorSequenceKeypoint.new(1,Color3.fromRGB(100,0,0))}) ree.Size = NumberSequence.new({NumberSequenceKeypoint.new(0,0.1),NumberSequenceKeypoint.new(1,0.1)}) ree.Texture = 'rbxassetid://867743272' ree.Lifetime = NumberRange.new(0.4) ree.Rate = 50 ree.LockedToPart = true ree.Speed = NumberRange.new(0, 2)

thing.Touched:connect(function(tou)
	if tou.Parent and tou.Parent:IsA('Tool') == false and tou.Parent.Parent:FindFirstChildOfClass('Humanoid') == nil and tou.Parent:FindFirstChildOfClass('Humanoid') == nil and tou.Name ~= "Blood" and tou.Parent.Name ~= "Projectile" and tou.Parent.Name ~= "big knife" and tou.Parent ~= player.Character and tou.Parent.ClassName ~= "Accessory" and tou.Parent.Name ~= "knife" then
		local pos = Vector3.new(thing.Position.X,(tou.Position.Y+(tou.Size.Y/2))+0.02,thing.Position.Z)
		thing:Destroy()
		if tou.Name == "BloodPuddle" then
			local reee = tou.CFrame
			if tou.Transparency > -0.2 then
				tou.Transparency = tou.Transparency -0.1
			end
			if tou.Size.X < 10 then
				tou.Size = tou.Size+Vector3.new(0.1,0,0.1)
				tou.CFrame = reee
			end
		else
			local bloodlol = Instance.new('Part',workspace)
			bloodlol.Size=Vector3.new(1,0.2,1)
			bloodlol.Name = "BloodPuddle"
			bloodlol.Anchored = true
			bloodlol.CanCollide = false
			bloodlol.Material = Enum.Material.SmoothPlastic
			bloodlol.BrickColor = BrickColor.new('Maroon')
			local cyl = Instance.new('CylinderMesh',bloodlol)
			cyl.Scale = Vector3.new(1,0.1,1)
			bloodlol.CFrame = CFrame.new(pos)
			local coru=coroutine.wrap(function()
				while bloodlol.Parent ~= nil do
					if bloodlol.Transparency < 1 then
						bloodlol.Transparency = bloodlol.Transparency+0.05
					else
						bloodlol:Destroy()
					end
					wait(0.1)
				end
			end)
			coru()
		end
	end
end)
local coru = coroutine.wrap(function()
	wait(1)
	thing:Destroy()
end)
coru()
end)
reeee()
wait()
end

end

function killz(playa,hitz,kneef,explode,pool,head,charred,override) local soundy = false local heyy = hitz if hitz == "UpperRight Arm" then local Limb = playa:FindFirstChild("UpperRight Arm") local ters = playa:FindFirstChild('UpperTorso') if Limb and ters then if ters:FindFirstChild('Right Shoulder') then ters["Right Shoulder"]:Destroy() end for i,v in pairs(Limb:GetChildren()) do if v:IsA('Weld') or v:IsA('Motor6D') or v:IsA('Rotate') then v:Destroy() end end

i cant post full script because of limit.

All the "Upper' i changed but it wont work help please It would be better to type in studio "Grab knife V3" Its a large script.