If these are coins that you sent to a blockchain.info wallet address then you should be able to send them directly using their web interface.

If they are coins you sent to an address that you have the private key for elsewhere then you can import this into blockchain.info through their web interface, and then send the coins on from there.

Some methods of private key import are fussy as to the format of the private key. If so then www.bitaddress.org is a great tool - the Wallet Details tab allows you to enter any format of private key, and does the conversions (all in Javascript on the client side, so you can run it offline in a disconnected computer).