The Billing Page in KnoCommerce identifies the plan the account is on and basic billing options.
Accounts for whom Billing is done through Stripe will have a 'Current Plan -> Next Billing Date' message at the top of the page. To view billing options for accounts billed on Shopify, check out the billing page on Shopify help doc.
Change Plan - View other plan options and make a switch to a higher- or lower-tiered plan option.
Manage Subscription - Make plan changes and/or make edits to Stripe billing information here.