I would think you'd need to pull your sdcard and use a card reader to put the ROM or update of your choice on it. Make sure its named update.zip and on the root of the card. Then place card back in device and flash like you tried to before installing update. If that wont work you'll need to find a guide for rooting your phone and follow most of those steps. This post would probably get more/better answers if posted in general discussion or help squad area.