You need to log in to Online Banking at onlinebanking.natwest.com (opens in a new window).
If you have more than one account, you can use the 'Quick Transfer' box on the 'Account summary' page. This will allow you to make an immediate transfer.
or
Select 'Payments & transfers' from the main menu, then on the Payments and transfers landing page, select the account you want to debit under 'Select an account'. Then under the 'Select who to pay' section, select 'Transfer money between your NatWest accounts' and follow the on screen instructions. Using this option, transfers can be made immediately or scheduled up to 120 days in the future.