Bitcoin transactions are irreversible. You cannot "cancel" a transaction. The best you can do is to create a double spending transaction which invalidates the original if it confirms. However that entirely depends on the double spending transaction confirming instead of the original transaction.

Since your transaction is currently unconfirmed, you can attempt to make a double spending transaction, but this may be very difficult for you as you are using blockchain.info. You will somehow have to get the private keys off for your addresses off of blockchain.info and use another wallet in order to create, sign, and send the transaction.