Updating the dongle firmware is a one time thing. If there is a dongle firmware update, I'm sure there will be lots of conversations about it in this forum.
When you connect your scanner to your computer and in Sentinel you go to Update>Update Firmware, Sentinel looks at the firmware version in your scanner, then compares it to the version on the Uniden server.
If there is a more recent firmware available, the newer firmware will be written to your scanner. You will see some prompts on what to do after that download.
If the firmware is up to date, a message will appear on your computer screen that you have the latest firmware.