How do i download the battlefield vietnam update

I cannot access any online features on the game. I understand that this is because i do not have the 1 gig multyplayer update. I know its supposed to pop up when i first load the game. But no such prompt has come up to allow me to download it. I have restarted the game, cleared my cache, and even redownloaded the game but still i have not been prompted to download the update. Can someone please help me so i can access online games.