Login to your account at https://www.dgauto.app/login
After you login, click the top right corner where your initials are and select "Billing":
After you click Billing, you will see an option to "Manage Billing" below your active subscription:
After, you will be brought to the billing screen. In order to upgrade or downgrade your package, you will select "Update Plan" or "Cancel Plan"
After you select "Update Plan", you will be able to upgrade/downgrade.
After you select "Cancel Plan", your recurring billing bill be automatically canceled and your credit card will not be charged any more. You will still continue to have full and unrestricted access to the application until the end of your billing cycle.