Clicking the 
edit action on the Transaction screen takes you to the Edit Transaction screen. Here you can edit the transaction content that has been imported.
Grey fields are not editable and dark blue fields are available to edit. To see a full list of the fields that are not editable (rather than just date and amount) click the expand arrow next to Amount.
Navigating between transactions can be done with the Prev and Next buttons.
To update a number of transactions at a time, Export the transactions to excel and use the Excel Sync functionality.