If you have saved a credit card within the software - that card is only visible to you.
This means that the payments against that card can also only be managed by you.
To remove a saved credit card, or stop auto-renewing a farm account, perhaps if you have sold the farm or moved to a different farm, this can be done from the "Billing" screen.
The Billing screen can be access from your drop down menu in the top right hand corner of the screen:
Each card has the option to be deleted.
In addition, below that section is one which allows you to manage which farm accounts that you have access to, you have setup for auto-renewal.