Select "File → Upload XML to Device", and make sure the "Upload additional file(s)" box is checked
Sometimes a Web browser may change the filename during download. In order for the .tar.gz to be properly installed, you must upload the file with its original filename. Uploading a file with a space in it (such as 2017-01-03-1400-RegiGate_400_7_ZEUS_3.12_07█(1).tar.gz ) will prevent the RediGate from properly installing the update, and may cause issues with future updates.
Also, do not unzip and upload the contents of the ".tar.gz" file; upload the original .tar.gz file with its full name and file extension.
After the upload, you device will reset and contain the latest firmware
You can confirm the version of software on your RediGate by logging into Putty. The screenshot below shows a RediGate with V:5.7.2016-12-29-1000: