Hi Paul,
Once downloaded you require to double click amd install it.
Where to depend on where you installed Radarbox to. If you followed the default install, just go with what the installer suggests.
If elsewhere you will need to direct the installer. Probably C:\Airvav Systems/Radarbox in the case.
To see if you are using the correct Navdata after the update go to File/database explorer/aircraft and on the bottom left of the window it should tell you around 192,644 aircraft in m/s
Alan