As far as I know the introduction of rules/procedures to ease the process of switching banks is imminent so if you can defer the transfer it may be worthwhile.
In the absence of new rules/procedures you need to open the new account and then time the cancellation of the old DDs (go into your branch and ask them to cancel them, they will most likely ask you to sign a form directing them to do so, and they will then cancel them on the computer), notify the payee in writing that you have cancelled the old DD, and then set up new DDs on the new account by sending a new DD mandate form to the payee. Be careful with certain DDs (in particular SSIA payments) in order to avoid problems with missed or duplicated payments (e.g. duplicate payments will jeopardise your SSIA if the cumulative amount exceeds the €254 per month limit). Once all payments have been moved you can close the old account.