My code is:
script.Parent.MouseButton1Down:connect(function()
local playername = game.Players.LocalPlayer.Name
local player = workspace:FindFirstChild(""..playername.."")
if player ~= nil then
player:FindFirstChild("Pants").PantsTemplate = "http://www.roblox.com/asset/?id=7133612447"
player:FindFirstChild("Shirt").ShirtTemplate = "http://www.roblox.com/asset/?id=7133614237"
end
end)
No Idea why this is not working, all it's doing is removing my clothing instead of giving me the new clothing.

2 comments
When asking/answering a question, be sure to encase your code in the Lua tags (Look for the Lua icon in the formatting tab). I did it for you this time.
Actually, Try to wear the shirt on the NPC, It will give the new ID, Paste the new ID from the Object to the shirt ID.