Updating your subscription from monthly to annual (or vice versa) is possible within your SpaceCraft Dashboard Account Settings.
1. Select Active Site in the Dashboard navigation bar
2. Select the Account button
3. Select Subscriptions under the Manage Account header, then select the blue Plan name on the righthand side of the website name to change the subscription
4. Select Change Plan Name (in this case it is Premium) to update the subscription to a new billing plan