Where can I change/edit Payment Methods?

Go to the Outlet Shops section.

Here click on the lower top navigation on My Store Account and below on My Outlets.

Then you will see your outlets, and here click next to your outlet on Dashboard.

Now you will see on the left navigation many tools to edit your shop and to add more info.

Click on Payment Methods and here you can only choose the option Paypal. Find all info in the text on how to add your paypal account to your Outlet Shop.

Please note, that you need to establish a business account on Paypal if you don't already have one.