To update your payment card details, log in to your Grubby account, go to 'Settings' then 'Payment details' and hit 'Edit' to enter your new card information.
Be sure to update the new payment details before the cut-off for your delivery.
These are:
Midnight Thursday for a Monday delivery
Midnight Friday for a Tuesday delivery
Midnight Saturday for a Wednesday delivery
Midnight Sunday for a Thursday delivery
Midnight Monday for a Friday delivery