Freesat 4K set top boxes should automatically update whenever a new firmware is available, normally automatically overnight as long as it is plugged in.
A Manual Way
With no “update firmware” option available via the Freesat 4K set top boxes system settings menu, this is how you can update the firmware to the most recent firmware available. (check in the menu / info page if you want the details)
1. Switch on your box
2. Go to Channel 999, You should see a Freesat Text Only Screen Leave it there for 15 minutes or more
3. Power Down the box (Disconnect at the wall or rear of the box)
4. Wait 30 Seconds
5. Apply the power again.
6. The box should start the update, and you will know its doing this as a Orange Progress bar will be shown under the Freesat Logo.
7. DO NOT SWITCH OFF - Wait for the box to reset itself and restart.
8. Check the Menu > System Info Page to see if the Version / Update Date has changed
If nothing happens you can repeat the steps and I suggest checking the Current firmware / software versions here
https://www.freesat.co.uk/help/4k-tv-boxes/software-updates