Visit https://docs.cradlepoint.com/r/modem-software-downloads-release-notes.
Scroll to your modem and click the software image you wish to download.
Save the file to a folder on your computer where you can easily locate it later.
Do not select the option to Open or to Run the downloaded file. Your dialog may appear differently, depending on your browser.
If you never get a save prompt, your browser may be configured to automatically send files to your Downloads folder.