Generate a new address. Send your Bitcoin from your other addresses to that new address in one transaction.
Note: I didn't understand the blockchain part (first line) of your post.
He's talking about the blockchain.info wallet.
Mitchell moved the thread here, it was originally posted on another forum and I don't think we can assume it's the web wallet because of where the post is.
Also, the way OP phrased "based on the old blockchain" makes me think otherwise.