To re-broadcast your tx, first get the raw transaction.
Open bitcoin-qt, click "Help, then click "Debug window" and click "Console".
Enter "getrawtransaction
Copy the long strings and enter it on http://blockchain.info/pushtx
Thanks for your help. Yes, I'm using bitcoin-qt.
Can I delete this tx if I don't want to rebroadcast and send it. I can't make sure whether the exchange can get the coin because I have generated a new address in the exchange platform.
If you stop broadcasting it, it will never get around the nodes/network. Have you seen how you can re-import your wallet? Then you old transaction will be gone and no longer broadcasting.