How would you make a gui change pictures when an NPC dies?

I've tried to do this by using _G variable in a respawn script in order to signal when the NPC died, but this didn't work on the live game.

The respawn script was a regular script and the gui script was a local script in the starter gui of a player.

Could someone give a quick example? The basic respawn script is below if that helps, I'm pretty sure it has all the necessary parts.

target = script.Parent:Clone()

function Dead()
	local respawn=target:Clone()
	respawn.Parent=script.Parent.Parent
	respawn:MakeJoints()
	script.Parent:Destroy()
end
script.Parent.Humanoid.Died:Connect(Dead)

So you'd need to create a RemoteEvent to be able to pass the death event to the client.

--Warning: Untested code! I'm typing right into this SH answer!
local event		= game.ReplicatedStorage.RemoteEvent
local target	= script.Parent:Clone()

function Dead()
	local respawn	= target:Clone()
	respawn.Parent	= script.Parent.Parent
	respawn:MakeJoints()
	script.Parent:Destroy()
	event:FireAllClients()
end
script.Parent.Humanoid.Died:Connect(Dead)

This will now fire the event to all the players that the Humanoid died! Now, we need to handle that on the client!

local event	= game.ReplicatedStorage.RemoteEvent

event.OnClientEvent:Connect(function()
	print("Humaoid died!")
	--Change the GUI
end)

Please remember to upvote if this helps, and accept this answer if it works!