The full installer contains an embedded Java Run-Time environment and is much larger than the update installer. Beyond that, the update installer is exactly the same and the full installer. If you have already installed Secutor Prime (including license-activated versions), you can download the update installer to get to the latest version.
The Update installer is provided for those organzations with computers running Secutor Prime that do not have access to the Internet. Organizations with Internet-accessible computers can keep Secutor Prime updated using the auto-update features of the product.