You can download our Offline Installer Package from a machine that is connected to the Internet, then transfer to your production computer that is not connected to the Internet using a flash drive or other storage media.
Here's a Knowledge Base Article on how to get set up for the Offline Installation Package if you see "Need Offline installer?" instead: Offline installer You can then go to Preferences ► System ► Installation to set the radio button for "Offline installation". Use the browse button to open a dialog to search for the location of the unzipped offline installation package folder. After that, you should be able to check for updates from the Updates tab of the Extensions and Updates page, or install new extensions from the purchased tab, and even modify the Core Feature Set.