stripe javascript subscription billing

Hi, I currently subscribe customers manually in the stripe dashboard for monthly payments. Which is ok. Sometimes their credit card expires and they receive an email with a link to a page with a form on my website asking them to update their card. The problem is, my form is just creating a new user in stripe. Instead I would like the form to add the new credit card to the existing user in Stripe. Why? 1. because then I would not have to manually subscribe them again each time they updated their card. 2. I wouldn't have multiple duplicate users.