You can add worker nodes to a cluster at any time in the Customer Portal:
Simply choose server configuration to add new nodes:
You can remove worker nodes from a cluster at any time in the Customer Portal. Servers removed from a cluster stay in your account; they are accessible in the "Dedicated Servers" section of the Customer Portal and require operating system reinstallation. You need to cancel the servers manually if you are not going to use them and don't want them in your bill.