When a transaction is Batched, the transaction can only be modified from the batch.
From the Toolbar select Sales Ledger.
Click Postings.
Locate the Batch (the batch number is found on the Transactions Header)
In the bottom half of the screen click RMB select Add Items to Batch.
From here you can modify or remove transactions if the batch is not posted.
The batch can be posted from the RMB menu on the Batch Header.