You may have seen the delete button on the site- this is for deleting the pdf. There are some conditions on deleting:
1) You must be the uploader of the document
2) No one else may have signed the document
You can not delete a transaction (eg signing record) from the blockchain.
One of the features of the blockchain is 'immutability'. This means that once a transaction has been confirmed by the network, it can not be removed or altered.