You can change your ShopTill-e Subscription Plan at any-time by clicking the 'Change your plan link' Active cards and invoices are shown. To add a new payment card to pay your subscription click the 'Add new card' button at the top of the screen:
After clicking the add new card button enter complete the form:
A summary of each invoice is displayed after clicking the pencil icon next to each invoice. From this screen you can access a 'Printable version' of each invoice: