I think that by default you will automatic be rebilled if you initially paid with a credit card.
In the control panel's Billing -> Make Payment sub-tab you can choose if you want DreamHost to charge your credit card if you have a balance due.
You can also remove your credit card information if you prefer so.
If you want to cancel your account you can do it from the Billing -> Change Plans sub-tab.
You can get rewards too: Earn FREE HOSTING through DreamHost Rewards!