Updating ListBox-element


I’we created a listbox element the following way:

	local Params = {}
	Params.Label = "Weapons"
	Params.Height = 150
	Params.Options = {} 
	for k,v in pairs (spawn_wpns) do 
		Params.Options[v] = {}    
	Panel:AddControl ("ListBox", Params )	

The menu is initialized in the following way:

local function LoadMenu()
	spawnmenu.AddToolMenuOption("Utilities", "Admin", "WeaponOptions", "Weapon Options", "", "", weapon_menu)
hook.Add( "PopulateToolMenu", "PopulateWeaponMenu", LoadMenu )

Then I have a button, when I click on that button the ‘spawn_wpns’ array/table is updated (addet a new element). So my question is;

How do I update the listbox-element? I need it to be updated when I click a button.