How Do I Make a Armor Script without a Localscript?

ISSUES

connect is deprecated in favor of Connect

:Remove() is deprecated in favor of :Destroy()

":findFirstChild()"should have a capitalized F -- :FindFirstChild()

HopperBin is deprecated in favor of Tool

Hat is deprecated in favor of Accessory

FormFactor and SurfaceType are Enums, not strings

GENERAL PRACTICE

You can use the for-loop in pairs to iterate through a table without the [#]

Use WaitForChild rather than FindFirstChild to get a variable you will be using later in the script (since you cannot change a nil value)

REVISED

Server Script

local r = Instance.new("RemoteEvent")
r.Name = "ArmorChange"
r.Parent = game:GetService("ReplicatedStorage")

local d = true

r.OnServerEvent:Connect(function(p)
	if d == false then return end
	d = false
	
	local defend = p:WaitForChild("Armor"):WaitForChild("Defend")
	local hitpoint = p:WaitForChild("Armor"):WaitForChild("HitPoint")
	defend.Value = defend.Value + 3
	hitpoint.Value = hitpoint.Value + 15
	
	local c = p.Character
	for i, g in pairs(c:GetChildren()) do
		if g:IsA("CharacterMesh") or g:IsA("Accessory") or g:IsA("Pants") or g:IsA("Shirt") then
			g:Destroy()
		end
	end
	
	game:GetService("ServerStorage"):WaitForChild("HeavyIronArmor Left Arm"):Clone().Parent = c
	game:GetService("ServerStorage"):WaitForChild("HeavyIronArmor Left Leg"):Clone().Parent = c
	game:GetService("ServerStorage"):WaitForChild("HeavyIronArmor Right Arm"):Clone().Parent = c
	game:GetService("ServerStorage"):WaitForChild("HeavyIronArmor Right Leg"):Clone().Parent = c
	game:GetService("ServerStorage"):WaitForChild("HeavyIronArmor Torso"):Clone().Parent = c
	
	local h = Instance.new("Accessory")
	h.Name = "Helmet"
	
	local hp = Instance.new("Part")
	hp.Name = "Handle"
	hp.Parent = h
	hp.Locked = true
	hp.FormFactor = Enum.FormFactor.Symmetric
	hp.Size = Vector3.new(1, 1, 1)
	hp.TopSurface = Enum.SurfaceType.Smooth
	hp.BottomSurface = Enum.SurfaceType.Smooth
	hp.Position = c:WaitForChild("Head").Position
	h.AttachmentPos = Vector3.new(0, 0.3, -0.03)
	h.Parent = c
end)

Local Script

local tool = script.Parent
local r = game:GetService("ReplicatedStorage"):WaitForChild("ArmorChange")

tool.Equipped:Connect(function(mouse)
	r:FireServer()
end)

tool.Unequipped:Connect(function()
	tool:Destroy()
end)

Move your "Armor" parts to the ServerStorage, change the "HopperBin" to a "Tool"

The scripts above create a RemoteEvent for you, make sure the local script is under the tool, the server script can be under ServerScriptService.