Enable automatic updates for your theme from step 1 in Appearance > WikiPress Setup Assistant and enter the code from your download receipt (also available in Launch and Sell Account page). This can be done at any time. Click Activate to activate automatic updates and support.
You can manage active site(s), disable sites when transferring to new domains from your Launch and Sell Account.
When a new version is available it will show as Update Available from the Appearance > Themes view.