Your Account Owner (or other Admins) can select the default policy within your Account Settings. You can learn more about Admin user permissions and how to request them here.
You can set a payment policy as the "default" payment policy by clicking the "✪" icon located to the left of the Payment Policy Label (i.e., title). Scroll to the top of the "Payment Policies" section to review this.
Note: This default will only apply to projects created moving forward. It will not adjust the default on existing projects.
Want to change the Payment Policy on just a particular project? Click here.