How to intensify effect then remove on death?

This is a local script that activates the blur effect once the client reaches a certain amount of health. From then on the I planned on increasing the intensity or "Size" of the blur as the health lowers and once the player dies I used the Died event to remove the effect. Two problems: As the health decreases the intensity only decreases instead of increasing and the second problem is that each time the character dies, the previous instance stays and another is put in place.

local plr = game.Players.LocalPlayer
local char = plr.Character or plr.CharacterAdded:wait()
local effect = Instance.new("BlurEffect", workspace.CurrentCamera)
effect.Enabled = false

local Humanoid = char:WaitForChild("Humanoid")
Humanoid.Changed:connect(function()
	if Humanoid.Health <= 75 then
		effect.Enabled = true
		effect.Size = 20 + (Humanoid.Health)
	end
end)


game:GetService('Players').PlayerAdded:connect(function(player)
	player.CharacterAdded:connect(function(character)
		character:WaitForChild("Humanoid").Died:connect(function()
			workspace.CurrentCamera:ClearAllChildren()
		end)
	end)
end)

For your first problem your math was WAY off. you were saying add the health to the size which will make size bigger as you heal. This makes it so it takes the absolute value of health - 80 and uses the absolute value of 20 - that. Adjust the equation as you want. Now for your next you added a lot of unnecessary functions, you just need to wait for char to die, thats all.

local plr = game.Players.LocalPlayer
local char = plr.Character or plr.CharacterAdded:wait()
local effect = Instance.new("BlurEffect", workspace.CurrentCamera)
local Humanoid = char:WaitForChild("Humanoid")

effect.Enabled = false

Humanoid.Changed:connect(function()
	if Humanoid.Health ~= 0 then
    	if Humanoid.Health <= 75 then
       	 	effect.Enabled = true
       		effect.Size = math.abs(20 - math.abs(((Humanoid.Health)-80)))
		end
    end
end)

char.Humanoid.Died:connect(function()
	workspace.CurrentCamera:FindFirstChild("Blur").Enabled = false
end)