:TweenPosition instead of just Position?

--\\ Services
local ReplicatedStorage = game:GetService'ReplicatedStorage'
--\\Nicknames and Tables
local ply = script.Parent.Parent or game.Players.LocalPlayer
local Event = ReplicatedStorage.ChatEvent
local Messages = {}
--\\ Functions
local function TweenPushMessages(Size)
	for i,v in pairs (Messages) do
		v.Position = v.Position - UDim2.new(0,0,0,Size)
	end
end
--\\FireServerFunction
ply.Chatted:connect(function(msg)
	if msg ~= '' then
		Event:FireServer(msg)
	elseif msg == '' then
		return
	end
end)
Event.OnClientEvent:connect(function(ply,msg)
local MSG = script.Messages_:Clone()
			MSG.Message.Text = msg
			MSG.Message_Owner.Text = '['..ply.Name..']: '
			MSG.Parent = ply.PlayerGui.ChatGui.Frame
			MSG.Message_Owner.TextColor3 = ply.TeamColor.Color
			TweenPushMessages(MSG.AbsoluteSize.Y)
			Messages[#Messages+1] = MSG
end)

The function TweenPushMessages is where I'm trying to do it, but I know it wouldn't work, would there be a way to recreate it with TweenPosition instead?