1. Go to Manage Subscriptions
2. Click on the subscription you wish to change the product for
3. Click on Replace this with another product
4. Click Change under the product you wish to change to.
5. Choose the order interval you want the new product to be shipped after
6. Click on Change Product

- Please note that changing subscription products means that from the time of the change you will stop subscribing to the previous one and start subscribing to the one you have chosen to switch to.