I hope this is the right spot. I want to order one of the plans here and pay monthly, but when I go to check out it has me listed as paying all of it upfront. Where do I go to change how often I pay?
Once you pay for the plan you can change the payment options via the control panel. Initial payment is upfront, after that you can pay via a number of different ways, periods etc..
It sounds like you may have just clicked the wrong initial button when signing up for how long you wanted to pre-pay for. Just try going to https://panel.dreamhost.com/signup/ and clicking the "one month" option for the plan you wanted!