New versions of ArcGIS Server Cloud Builder on Amazon Web Services are currently released at the time of every ArcGIS update. The most recent version of Cloud Builder creates new sites with the most recent ArcGIS update applied and using EC2-VPC instances, unless you are creating a site from a template. When you create a site from a template, the version of software used in the template and instance type are applied to the new site.
You can download the latest version of Cloud Builder from My Esri. You can access the download if you have purchased ArcGIS for Server.
If you update your Cloud Builder installation to ArcGIS 10.3.1, you must first uninstall your existing Cloud Builder installation and install the 10.3.1 version of Cloud Builder.
Update notices and restrictions
If Cloud Builder detects that you are not running its latest version, you'll see a message that an upgrade (in other words, an update) is available. Get the update only after you have determined that you are finished creating new sites at your current ArcGIS version. Once you have accessed your Amazon account using a particular version of Cloud Builder, you cannot go back and access your account using an older version of Cloud Builder.
When you update Cloud Builder, the version numbers of your existing sites and templates are not affected. You can still manage your existing sites and templates in the updated Cloud Builder. It's possible to see sites and templates of differing versions listed side by side in Cloud Builder.