From LightWiki

In Layout go to the Help menu in Layout shown here and choose the Enter License entry. (in 8.2 and versions 7.5b, c and d; you'll have to look for the tool in the Utilities > Additional menu under the name Make License.key. In previous versions of LightWave this script was not available and other methods need to be used to enter the license.key).

This will bring up a window like the one shown and you can paste the number you received from NewTek Europe into it and hit OK.

Now close LightWave and restart it and all should be well...

If you still see the LW9 splash screen asking to register when you start up LightWave:

• Edit your license.key file in Notepad. You can find the license.key file in the same folder as the main LightWave program files, make sure there's only one line (no extra blank line or second 'discovery' key)
• check if your dongle driver is current. If not, head on over to the sentinel site, unplug the dongle and install the new drivers, then re-insert the dongle. The drivers can be found here: Sentinel drivers (you will need to click on the Sentinel SuperPro link on this page).