listunspent
Go to blockchain.info, and paste the "txid"
Check the public address of yours that received the funds, copy it.
Back in the console of QT (you may need to use walletpassphrase before if you encrypted the wallet):
dumpprivkey your_address
Back to blockchain.info
If you already have a wallet there, just import the private key using the import feature (and pasting the result of the dumpprivkey command). If not, create a wallet before importing.
From the blockchain wallet, send the coins to wherever you want.
Once the unspent output is clear, you can remove the private key from blockchain wallet (you need to archive it first, I think).
If that fails, please specify at which step it did, please.