To buy or renew an existing Parallels Access for Business subscription, log in to your Parallels account.
Go to Parallels Access > Corporate Subscriptions.
If you don't have a subscription, you will have the option to buy one.
If you have a business subscription for Parallels Access, here you will be able to manage its auto-renewal and other subscription properties.
For instructions on purchasing a regular Parallels Access subscription, please see KB 116724.