The removal or changing credit cards can be done in Your 2degrees but requires deleting the Monthly Auto-Top-Up (MATU) and/or entering a new cards details and selecting that card as the current one.
Here's the process -
1. Login to Your 2degrees.
2. Click on Top Up in the navigation menu, then Manage Payment Options
3. Click on Automatic Payments.
4. To remove the MATU immediately > Click 'Remove' and you'll receive a confirmation.
5. If however you want to -
Change the amount
Change the day
Click Edit > Make required changes > To save click on 'Set up my auto top up'.
Hope that helps.