I can't do that between lines 1 and 2 to create a script which, after leading the slider to the end of the bar, removes the entire GUI. If you need the final position of the GUI just write "XYZ".

local UserInputService = game:GetService("UserInputService")
local Dragging = false
script.Parent.TextButton.MouseButton1Down:Connect(function()
	Dragging = true
end)

UserInputService.InputChanged:Connect(function()
	if Dragging then
		local MousePos = UserInputService:GetMouseLocation()+Vector2.new(0,36)
		local RelPos = MousePos-script.Parent.AbsolutePosition
		local Precent = math.clamp(RelPos.X/script.Parent.AbsoluteSize.X,0,1)
		script.Parent.TextButton.Position = UDim2.new(Precent,0,0.5,0)
		game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = Precent*100
	end
end)

UserInputService.InputEnded:Connect(function(input)
	if input.UserInputType == Enum.UserInputType.MouseButton1 then
		Dragging = false
	end
end)