For best results enter one or two keywords related to what you are looking for
If you want/need to change your payment details there is only one way to do it.
This is the best way to change your details, remember if you top-up early you wont lose out as all top-ups will extend your top-up date from the current top-up date.
Go to the top-ups page and click the buy button for the amount you wish to top-up.
You will be asked to choose an existing payment method or use 'change payment method' to enter new details
Click on 'change payment method'
Enter your new payment details and pay for your top-up
Future top-ups will default to the payment you have just used